THE JOURNAL OF THE

Society of Dyers and Colourists Vol. 60-No. 5 MAY 1944 la& Month&

Proceedings of the Society ~ ____

MANCBSTER SECTION

The Dyeing of Viscose Rayon Yarn in Cake Form

Meeting held at the Urtmd Hotel, Mancheater, on 16th October, 1043, Mr. C. M. WILXJAMEJ in the chair.

C. M. W E ~ A R E R

The annular peckage produced in the centrifugal spinning box invented by C. F. Topham in IBOO for the spinning of viscoae rayon yarn ia known throughout the rayon trade as 8 “cake”.

In the past. vieOoae rayon producers wound the wet cakes into skeine prior to desulphurising and bleauhing. More recently. however, these wet proceases have been carried out with the yarn in cake form, with a consequent reduction in labour costs and a marked improvement in the quality of the yam. This practice h&s resulted in the almost complete cessation of deliveries by Courtauld6 Ltd. of Vieooae myon yarn in skein form.

As the result of dyeing viscose rayon in cake form, many technical advantagee are gained in subsequent processing, viz.- (1) One operative can supervise the winding of more dyed cakes than dyed skeins, whilst leee time is taken to train a cake winder than to train a skein winder. (2) There is leee winding waate. (3) Oake-dyed yarn is superior in quality to skein-dyed yarn. (4) There axe fewer knots on the cones. (6) The rate of production in weaving and knitting ie higher. This development in viscose rayon manufeatiure hae

presented the skein dyers with the problem of undertaking the dyeing of visOoee rayon yarn in package form, and i t in with the object of giving some p b c e in thh matter that the Directors of Courtaulde L a . have coneented to the publication of the present paper, which is based on the prautioal experience of dyeing 1,600,000 Ib. of viscose rayon cakes.

The development of dyeing in cake form waa a logical, inevitable, and progremive stel, in the processing of viscose rayon, and i t may possibly be wondered why it did not occur earlier, but it must be appreciated that cake dyeing is 8 comparatively new method.

At Droyleden, the flrat batch of cakes, weighing 188 lb., waa dyed on the commercial scde on 8th January, 1037. at the time of the demand for end-and-end gold and white warps, which formed a very convenient outlet for the initial bulk dyeings, since any unevenness could not be Been in such warps. The present author’s colleagues at Coventry had been at work on the problems wsociated with the wet proceeeing of cakea for some years previously, and it WBL~ only their succese which rnade the subsequent dyeing of cslres leeible. The fire$ problem in oome%ion with tlp dyeing of

vimm rayon cakes is the machine. In the early ex eri- ments at DmyMen 811 mrtu of method were tried wkich, ip retroepeot. a peer to be more amusing than mrioue. Thus, the dyetquor waa sprayed continuously into individual rotating spin boxes; or the spin box waa inverted and rotated in the dyeliquor itself; or cakes were dyed on vertical and horizontal perforated tubes, with

(A2)

and without formers; or cctkes were dyed in f01t111 baths; or cakes were dyed packed like bricks in an Obermaier machine, and repacked and repacked until penetrated.

Finally, the machine used at present was evolved and, although i t is not considered to be the last word in machinee, i t serve# its purpose. This machine, which is illustrated in Fig. 1 (p. 110), wm designed by combining different idem from many types of machines, and i t WRR built for Courtaulda Ltd. by the Longcloso Engineering Co. Ltd., by whom it is marketed.

The maohine ie of stainless steel, with D water-sealed centrifugal pump, valves and pipes for two-wDy circulation, and with an expansion tank in the circuit. The double- bottom container holds from 6 to 42 perforated spindles placed verticelly. Each Bpindle haa a screw thread nt each end and is screwed into the container, and, therefore, may be removed or reversed as required. The containers m8Y be lifted bodily out of the machine by means of i ~ i e h t r i c crane for loading and unloading, wlrilHt duplicate containers for each machine enable one container to he unloaded and reloaded while another batch is baing dyed.

The spindles on the large machine take 9 (mkes, those on the medium sized mechine take 7 cakes, and those on the smallest machine (85 cakes capacity) take d cakeri, from which i t is evident that the capacity of tl ic InrgeHt machine (42 spipdles) is 378 1-lb. cakes.

These machines were deliberately designed to be very elastic in respect of the weights of material they would take. In order to achieve this purpose, each spindle is blanked off at one end 80 that, if the spindle hm no cakes on it, circulation of the liquor through that particular spindle may be prevented by simply reversing i t and screwing the blank end into the base of the container. Further, if the weight of material ordered only fills part of one spindle. the spindle may be completely filled by adding tho necessary number of non-porforated cake holders, thus giving perfect adaptability for broken weights of material.

Experience at Droylsden has shown that the results are better with large batches than with small batches. ThiR is attributed t o the fact that the influencu of leakage caused by ill-fitting, collapsed, or distorted clikos is not so great in a large batch as in a small one. Baaed on this experience, cake dyeing is not undertaken for lots smaller than 26 cakes to a shade.

A laboratory-scale machine which will take 1 or 2 cakea is also available. This machine is useful for small-scale tests, but it has very definite limitations. One of its merits is that the results are always poorer than similar d einge in the large machines, 80 that, if a fair result is o&ained on the laboratory machine, 8 good result will be obtained in bulk with the same dyes.

WHITTAKER-"DYPI:IN(X OF VIBCOBE RAYON YARN IN OAKE FORM" M a j ~ 1041 - .~ - __ 110

The cake holders used are made of bakelite and aro perforated; the preferred type is called a "window" holder, and has 6 large holes in t,he centre of the barrel of the holder. Another type is drilled with a large number of small holes which should not be carried right to the top or bottom of the holder. If the cake fits wcll on the holdor, the style of perforation does not matter, and the cake will dye satisfactorily with only one large hole in tho barrel of the holder. Each cake is mouutedaii a separate holder, and the holders are stacked one upon another. The top one is fitted with a lid which permits the column of holders to be screwed tight to the spindle by means of

and back pressures, but circulation from outside to inside is never so consistent, duo to variable leakage. Circulation is always started from inside to outside, and the 6nal circulation before lifting out of the dyeliquor is from inside to outside, because t h i H frecs the cakes from the holders and so facilitates their removal. The periods of circulation are 20 min. from inside to outside, and 10 min. from outside to inside, throughout the dyeing.

With euay levelling dyes, e.g. Chlorttzol Fast Orange G (I.C.I.), many sliaties may be dyed with inside to outside circulation only. In bulk dyeing, however, dyed lots frequently show cnkos which aro tlefinitely lighter 111

F I G . 1

a suitttble nut. The cakes inuat be well fittud oil the holders, and girls are most suitable for this work; if the cakes are badly fitted, a bad result is highly probable. Now that the cakes supplied by Courtaulds Ltd. are (4nd will be) of standard size, it is poseible to obtain good fitting, but if the dyeing is prolonged, 0.g. to 6 hr., a few collapsed cakes may be anticipated, although it does not always follow that a collapsed cake will be poorly ene- trated. Penetration will depend on the stage o r the dyeing at which the cake collapsed; if i t collapsed a t an early stage, it is unlikely to be properly penetrated.

Two-way circulation is advised, although circulation from inside to outside is considered the more efficient. Moreover, theoretically, two-way circulation reduces the thiokness of the package to one-half. The pressure when ciroulating the liquor from inside to outside runs con- sistently with a difference of 4 Ih. between the forward

shade on tho outaide to u depth of u !ow threads, but circulation from outside to inside for 10 min. correcta this defeot.

The dyer of cakes, unlike the skein dycr, ccmnot see the material being dyed, and 80 cannot estimate the degree of penetration and evenness of the resulting dyoing; he is therefore always in a state of considerable anxiety as to the auccesa of hie dyeings. Thorough examination of cakes for evenness of shade and penetration depreciates their subscquent windability, and this fact limits the number of cakes which may be exarniiiotl bofore R b u t c s h IS despatched. It requires great skill and judginorit to examine a cake with the minimum of disturbance and to say whether it is evenly dyed, as well as completely penetrated. At Droylsden this work is done by girls *whose touch is much more delirate than that of a man; they are, therefore, much more skilful in re-forming tho

Alov 1844 WH1TTAKER“DYEING OF VI&COSE RAYON YARN IN CAKE FORM” 111

cake after exuminution. The examination Is d&le’sU the wet st,ate, after the cake has been’h droextracted subsequent to final matching, and before the Lt is unloaded from the machine.

It is our experience at Droyladen that, if chctllnelling occurs in a rake, thereby producing white places ,due to lack of penetration, circulation of the dyeliquor may be continued indefinitely without covering the white places. There are two ways of correcting this fault. (1) The cakes are taken off the holders, hydroextracted and then put bark again on the holders, when they will usually be rorrected perfectly after a further very short time in the dyeliquor. The correction is due to the fact that handling and hydroextracting alters the lay of the traverse and thereby re-forms the cakes, so that the channelling due to the initial deformation is removed. (2) In extreme cases i t is advisable to dry the cakes as well. A faulty lot of cakes which has been dried has always responded to correction, but increasing experience has shown that fiiulty penetration can usually be corrected merely by hydroextracting. When dry, a little yarn is wound on aepn,rate bobbins from the outside, middle and inside of one cake. Them hobbins are knitted on a single-thread knitting machine in successive panels of outside, middle and inside, and the resulting knitting gives B very good guide &B t o the evenness and penetration of the shade. although, of course, the test is actually representative of only one cake. Incidentally, examination in white fluorescent lighting is better than examination in average daylight for revealing faulty dyeing.

The problem of paokage dyeing has two aspects, viz. mechanical and technical. The mechanical aspect has been deelt with first, because correct dyeing presupposes circulation of the dyeliquor through the packages in 8s nearly uniform a manner &11 is possible from an engineering point of view.

The present standard weight of the cakes supplied by Courtaulds Ltd. is 18 oz. which, under the exigencies of wartime labour shortage, sometimes rises to 8 s much as 20 oz. It is definitely intended, however, that the oakes shall be considerably increased in weight when the requisite alterations to the spinning machines can be made.

It will be immediately realised, therefore, that a water supply of good quality, free from sediment, is absolutely eesential, and it will also be appreciated that the finer the filament denier, the greater the need for pure water. Manchester Corporation water is used at Droylsden, but it is found necessary to use in addition a dispersing agent, e.g. Calgon, since exporience has shown that the cakes are liable to be dirty if Calgon is not added. The use of 4 oz. of Calgon per 100 gall. of li uor circulated through the cakes has been made standarj practice.

The time of dyeing varies from 24 hr. to 6 hr., according to the nature of the dyes, the depth of shade, and the filament denier of the yarn. Consequently, it must not bo forgotten that Calgon is liable to develop acidity on prolonged boiling.

It still remains true that the major portion of viacose rayon is dyed with direct cotton dyes. Further, the prohibition of tho production of furnishing fabrics during the war has substantially reduced the demand for vat dyed shades on rayon, so that our experience of cake dyeing has becn largely confined to dyeing8 with direct cotton dyes.

The liquor-goods ratio in the machines when fully loaded averages about 18:l. but this is not the most meterial

The point to be remembered ie that the effective point iquor-goods ratio a t the face of the stationary threads in the cuke, which is where the dyeing takes place, is not more than 3:l.

Passing to the dyeing aspect, it must be realised that the use of concentrated dyes in order to control their salt aensitivity is not suffloient unless the water being used is reaRonably free from electrolytes. A water of initial hardness of, for example, 28”, even if Permutit-treated, is not to ‘be recommended for cake dyeing, because it entails working continuously under a most severe handicap, the removal of which could only be effected by means of e retarding agent for direct cotton dyes effective in water heavily charged with electrolytes. No such retarding agent is known to the present author. On the other hand, it is not, necesmrg t n ~ I R C Rn elertrolyte-free water, ~ i i ~ l i n~

A viscose rayon cake is a most efficient filter.

.

that obtainable by the new double resin t,reatment of the Permutit Co. Ltd. Munchester Corporation water is used at Droylsden, and both Clasgow and Bradford waters are equally suitable. It is the type of water which is frequently met with in the Midlnnda and South-East England that is not very suitable for cake dyeing.

The present author and his colleagues huve written so much about the individualism of dyes, salt sensitivity, and the use of that best of ull dyeing assistants, comrnonsenae, that i t is now hardly necessary to clisruss these topir8 further. In addition, it is pleasing to note thut the dye manufacturers are now responding to the frequent uppeals that they should piihlidi the requisite information about their own dyes. In the caw of at leasb one firm the eyes of the staff concerned have been opened to properties of their own dyes about which they were ignormt, and the new data have proved of definite commercittl advantage in ehowing them that some of the mixings illustrated on their pattern curds were ludicrous ! It was also seen that some of their dyes were, like Rome of our journeys, “not really necessary”.

Unless the properties of the dyes being ubed are known to the cake dyer in respect of migration, rate of exhaustion and salt sensitivity, Ire is working blindly and deserves ~ l l the trouble which he will inevitably meet.

In a previous paper’, the direct cotton dyes were divided, from the point of view of package dyeing, into three classes, viz.-

Class “8” Dyes, which have a high rate of exhaustion without added common salt, but have a very low time of half-dyeing, SO that they level quickly.

Class “B” Dyes, which have a low rate of exhaustion without added common salt, but the rate of exheustion may be adequately controlled by carefully re$ulated additions of common salt based on their pre- determined Salt sensitivity.

Cluaa “C” Dyea, which have a high rate of exheustion without added d t and a time of half-dyeing which indicates that they cannot be expected to level quickly.

Class “A” dyes may be dismissed a t once by saying that they present no diaculty in normal usage. In fact, the dry dye could be rubbed on the cakes, yet they would be dyed level. These dyes are largely used for lingerie shades.

Cl&s “13” dyes present more difficulty than Class “A” dyes, since they must be applied uniformly because. of their low rate of migration. Commonsense control of the aalt addition enables them to be dyed without diEculty, but thereby lengthens the time of dyeing as compared with Class “A” dyes. With Class ”B” dyes, if an addition of dye hes to be made for shading purposes and the dyeliquor has had salt added to it, then the dyeliquor containing the salt must be run off and fresh dyeliquor containing no salt must be used for topping up.

Class “C” dyes have high rates of exhaustion without udded common salt, and times of half-dyeing which indicate that they must be applied in a level manner because of their poor rates of migration. This class of direct dyes is the most difficult to dye satisfactorily on cakes and requires (1) the highest concentration of dye commercially feasible, and (2) the adoption of temperature control.

Dyeing8 with Class “A” and Claw “B” dyes are always commenced at QOOc., because the viscosity of water at 90”o. is low in comparison with its viscosity at low temperatures; the freest circulation is therefore obtained at high temperatures.

YISCIJSITY O F WATER _ _ _ _ _ _ _ . _ _ _ _ ~ ~ ~ _ _ _

Tmilic-mt~rirv I Ylultllt~y ~ Tiw~wiit i irtt j “liidity (“c.) (recilrocal poia%~) ( ” c . ) (reeiprocnl yolacn)

20 09 I (10 213 246 2x0 315

:I0 I 124 I

40 152 5o i 1H2 QO

Dyeings with Class “C” dyes, however, must be com- menced at room temperature, and the temperature raised slowly and regularly to 9O”c. in the course of 1 hr. The following exhaustion figures for Benzopurpurine 4B Standard (9.) and Benzopurpurine 4B 180 (S.), both dyed in 10 vd . on 160/27 viRcose rnyan fni. 30 min. withoirt,

112 WHITTAKER-“DYEING O F VISCOSE RAYON YARN IN CAKE FORM’

addition of common aalt, illustrate the necessity for this precaution-

The results tabulated above are illustrated by Fig. 2.

Temperature (“c.)

BIO. 2

It is only the Class “C” type of dye which it is necessary to have in the most concentrated form commercially feasible. When supplied in such a highly concentrated form, some Class “C” dyes, e.g. Chlorazol Blue B525 (I.C.I.), may be put into Class “B”, because, as they have no affinity for the fibre without salt, their rates of exhaustion can be controlled perfectly by adding salt.

There is no necessity to purchase Class “A” and Class “B” dyes in the highest concentration, because the normal commercial branda are completely controllable, provided that they are not used together with Class “C” types, in which case the electrolytes present in the Class “A” or Class “B” dye might have a detrimental effect on the exhauation rate of the Class “0” dye.

The present author has recorded in a previous paper‘ how a mixture of 0.76% Benzopurpurine 4B 180 (8.) and 1.4% Chloramine Purple lOBC (S.) gave a great deal of trouble in package dyeing on account of the electrolytes present in the latter, which caused a 90% exhaustion of the former at 40’0.. a rate of exhaustion which rendered the dyeing uncontrollable.

The supply of batch-strength dyes may present com- mercial difficulties to the dye manufaoturers, but these difficulties are easily overcome with the goodwill of the dyer. The present author, when buying these con- centrated types, is prepared to accept (1) slight variations in strength from delivery to delivery, and (2) variations in the shade of successive deliveries. Them variations are overcome by buying a large quantity at a time, so that any inconvenience due to the changeover from one delivery to,nother of different strength and shade is infrequent.

l h e control of salt additions has been etressed 80 much that it ctppeam advisable to describe the method used at

Droylsden for making salt additions at 10 min. intervale. The following Teble shows the usual rate at which salt is added to salt-sensitive dyes of Class “B” which do not level easily and. therefore, muat be applied carefully. The various additions of salt are made at 10 min. intervals and the figures refer to a 100 Ib. lot of material.

- _ ____-____- - - ’ Wvlght of Coiuinoli 8nlt added (02 )

I.lylit Slitidi~e Dark Ylmdi’a Nuuibrr of I \ c h I i t i o i i R 1- -

The above procedure is a general guide, but alterations are made as required when a shade involves a mixture of dyes which is known to be specially salt-eensitive, or when there is a stage during the addition of salt at which the afflnity increases suddenly, thus indicating a danger oint requiring special precautions. The salt is weighedp out ready in separate paper bags in the above weights, so that the man in charge has only to watch the time intervals.

The above figures are suggested merely aa a guide, because individual dyes vary widely in their salt-sensitivity, as shown in Fig. 3.

loo

90

80

70

60

50

40

30

20

10

0.1 0.305 I 2 3 4 5

% Common salt added

Fro. 3-Salt senaitlvlty curves 160/27 Vlscose rayon dyed at 90%. for 30 mln. In 10 vol.

The minimum figures tabulated above are those em- ployed with the most salt-sensitive dyes, e.g. Chlorezol Fast Orange AGI (I.C.I.), but Pyralon Orange Q (L.B.H.). which has a much shorter time of half-dyeing, requires larger quantities of salt Again, many dye8 have a great salt-sensitivity up to a certain percentage of salt, but, when this percentage has been paased, larger quantities may be added without risk of unsatisfactory results. Experience at Droylsden hae shown that much leee salt is needed in bulk dyeings than in matching shades in 10 vol. in the laboratory. Thus, the salt used in the bulk dyeings of 11 shades previously matched in the laboratory was only one-quarter of the amount of salt found necessary in the laboratory dyeings. This point should be borne in mind when dyeing a new ahade in bulk for the first time.

Solubiliaed Vat D p - This claw of dyes may be dyed satisfactorily on viscose rayon in cake form within the limits of the depth of shade obtainable. The members of thie c l m are just as varied in their individualism as those of other olasses, and knowledge of their respective a W t i e s and salt sensitivitie~ is essential for succed.

The greatest difficulty experienced in bulk application has been due to occasional hydrolysis of the dyes during the prolonged time of dyeing, which is apt to give uneven results in the form of lighter-dyed threads. Soledon Jade Green XS (I.C.I.) is the most substantive member of this claas and requires most care in dyeing. Soledon Blue RCS (I.C.I.) is one of the least substantive end, therefore.

May lfill WHI'ITAICER-"DYEING OF VISCOEE RAYON YARN I N CAKE FORM" 113

may be dyed at higher temperatllres and with larger additions of salt.

The following two recipes, representing successful bulk tlyeings. illustrate in detail the methods employed a t Droylsdon, all percentages being b a e d on the weight of tho muterial, nnless otherwise stated-

( I ) Dissolvo 1.5% Soledon Yellow GS 40 paste (I.C.I.), 0.44% Soledon Jade Green XS 200 paste (I.C.I.), and 0.14% Soledon Green GS paste (1.C.I.) in water a t Wr., p w the solution through fine rlotlr and add i t to the cold tlyoliquor containing 1% soch ash. Enter the cakes dry, aircnlate the dyeliquor for 20 min. inside to outside and for 10 min. outside to inside, repenting this cycle through- out. After 30 rnin., raise the temperature slowly to Woo. in 80 min., using a cloned steam coil. Add common salt nt 10-min. intervals as follows- 3 additions of 0,57& salt, 3 additions o f 1% salt, 3 additions of l.hyo salt, trnd 3 additions of 2yo salt, making a total addition of 15% stblt.

A small sample'of the material is developed and exnmined for shade before the last addition of salt is made, and the cakcs are examined for penetration. If tho shado is satisfactory, the cakes are c h & q x d for 1 hr. with 0.5 g. sodium nitrite, 1 C.C. sulphuric acid (B.O.V.). turd 2 g. common stilt per 100 r.c. tfyeliquor. and then exitmined to see if the shade is fully developed. If satis- fwtory, the cakes w e washed off for 10 min. inside to outside, then for 10 min. outsido to insido, first with cold water, then with cold 5% soda ush; a warm wash is given next, followed by soaping a t 8 0 " ~ . for 20 min. inside to outside und then 10 min. outside to inside; finally, a wash is givon with 1 lb. soap and 4 02. Calgon per 100 gall. of dyeliquor for 10 min. inside to outside.

( 2 j Dissolvo 2.8% Soledon Yellow GS paste (I.C.I.), 1.97, Indigosol Brown 1l3H powder (I .G.) , and 1 % soclu ash in water. In this c a ~ e , dyeing is commcnccd a t 6 0 " ~ . Tho dyeliquor i H c*irrulated for 20 min. inside to outsido urul thon for 10 Inin. outside to inside. Salt is next tldtled at, 10-rnin. intervals as followt+- 3 additions of 2.59/, edt. 3 udclitionn of O.,b sd t , 3 additions of 7.6% mlt, 3 irtlditions of 101yo sirlt, and 3 additions of 15% salt, inaking a total addition of 120% salt. The shade is cle- veloped HH described ul~der Hecipe (1). The a f i i t y of these tfwo dyes is much lower than that of the dyes uaed in Recipe ( l ) , so more salt is required ctnd it may be add& iu Isrger quantities a t it time.

I'at Dyss- Experience of clpplying this class of dyes to viscose rayon cakm Iiw been less extensive than in the caw of direct cotton dyes. A large amoimt of experi- inontal work has been c!ctrrietl out, however, UB well 8s a liniitotl ni i inber of bulk ctyeings, antl the main conclusion is that the tempertrture of tho clyevat must be much higher than in normal dyeing practice, 90"o. being recormnundud. It is obvious thet C I ~ R of the Caledon Blue HC (I.C.I.) type must break down under them conditions, arid the inability to dyo this type of blue vat dyu is the rnujor problem tst the Inonlent. It must bo solved, because blue shutlos form such R large proportion of the vat-dyed sliatles in commerciel demand: Soledon Blue ltCS (I.C.I.) rnuy he used only for pale shades. The economy in winding antl thc quality of vat-dyed yarn are most satisfuctory after dyeing in cake form, and bulk shales litlve becn dyod in which there hae been less than 1% winding waste.

Atoic Uyea-- A linuted number of nzoic dyes have been dyed on viscose ruyon in rake form without any unusual difficulties. The method of application is the same aa that employod to obtttin penetration of thick cloths i.0. the "naphthol" is applied at a high temperature. After padding with the "naphthol", the cakes are washed with n strong Holntion of common salt, in order to reduce the temperature previous to coupling, und, after coupling. they are finished off in p a p in the usual manner, but using a filtration eystein, which is desirable in all pack machinee when soaping off azoic-, vat- and sulphur-dyed EhadeE.

Sulphur Dgea- With the exception of Sulphur Black, this clam of dyes has never been used at Droylsden to any ooneiderable extent, for two reasons, viz. (1) the difficulty of matching exactly, due to gradual dxidation on storing; and (2) the fact that sulphur dyes show up strongly any variations in the dyeing affinity of viscose rayon. Con- siderable trouble haa been experienced in obtaining SStiSfeOtOI'y Sulphur Black ahades on viscose rayon cakee, .(I

und it has beon found norosmry, in order to uvoicl light patches in the cakert, to employ toniperatiire control hy starting itt room temperut,ure and rc~ining the temperaturr gTadUally to the boil. Botliriin sulpliitlr i.rystulN ahoultl be used in machine dyeing.

PignlenI pudding- It is rhimeil t h r t the pigment padding of vat dyes, which hns been so largely ridopteti in piece dyeing, is suitable for the dyeing of packages. This method has been used a t Uroylscten in mriny experiments with visoom rayon cukes, and no dilficulty litis hoon experienced in obtaining even impregnation of the clrltex with dispersed vat dyes, which iH an indication of the great improvement effectud in m c n t years by clyentuff manu- facturers in the production of highly dinporsed vat tlycs. A difficulty has always arisen, however, when applying the reduction bath, in order to reduce nnd fix the vat dye on the fibre; the surge of tho rotluction liquor through the cake has always washed the diapersod vat dye off the fibres before i t ha8 had time to become fixed. In consequence, dyeing still has to be carried out in t,licr usual manner with reduced vet dyes.

Finally, dyers are warned against the tlnnger of drawing genflral concluaiona from a particular lot of dyed material. It is so eaay to blame the cake when, in foot, the blamct lics elsewhere. The dyeing of viscoso ruyon cake8 is still in an early stage of development antl it i H inadvisable, a t present, to be too dogmatic about it.

I Whittakcr this J a r . 1942 58. 253. 2 Whlttakrr: ibid., l93li. 54, 859.

" W W N C E S

DISCUSSION Mr. +red Smith asked the Lrcturer how Iir would account fur

a dye of the level dyeing Clms "A" tylw giviiiu HII uiiovim dyviiig. Tlic Lecturer explaini~d tlint cullaim of t h r cnkv iliight takt, ~~lnc l .

carly In the dyeing, and thin ooiild iiot be n w u uwliiu to the ~ n n c l ~ i i ~ r belu a closed one. If i t took plncr wlthhi t h r tlrat 5 win. the cakc wouh be lucked or pulled on to the opposite sidr dnd h i e ll uor woiild pour through the collapsed aide. The oth& side waul$ bo tlghtenrd, and i t was the ti lit aide which was not penetrated. Ex eri eirci! had proved that I n 8nc% cases unipliig could continue Indetlnkrly without producing ~horough penk&tlori of thv dye.

The exaiuple quoted was an exaggpratcd ~881' . Thrre would norinally be clianueUiiig, due to the Ilquor surging up. I f tlirre wan one cake which wnn solnewhat wtwkcr In the wnll than auy other cake on the samr splndIe that cake wiiuld blow aiid one portion of it would lock and would ;rot bc penetrated. But If the faulty cake were takcii out and Iiydmextmcted the chanuelliiig would IN! stopped.

~ r . A. Willlama, coinrnentiiig oil the i,eaturcr'a stutcnicntn that 11 laboratory machlnc would not glvr similar rtaiilts t o a 42-splndlr insohint?, suggested, as the roisult of an expurli-iti:c Iir had had 8onw ytwn ago, that If there was a aliiiitar volunio of liquor 111 both cwr8 bhe ltrborator &achlne- would bib an effectivr as tlw 42-splndlr Iuacllliie: Hc dld not &sagrw with the Lrctiirer's sf atmeri t thnt the ainouut of liquor in contact with the yarn wns whnt matt,rred, but what he

I t wna ncrrsaary to use H laboratory uiwtiitir wliirti wciu~t~ give viacttv ttir uninr liquor-goods ratlu, and thc rxprrinirntcr cotirwned ha& In that WHY achieved cxnctlv the sainr reaults with thr full niuohiii?

had 8tHtCd Was proved to be the CWt! HOllll' yrers IIKO in c o p dveing.

wi!p 100 Ib. of cops. lhi8 Lecturer replied by nnkliig why the 5-apii1dlc iii;ictiiilr dld

not glvv the snmr results HH the 42-splndlr ninchiiiv whcti thc' liquor. goods ratio was the same in both cases Y

Mr. 6. B. Adanis reierred to the wiuding of thr caki-s nnd said he itnsiinied that thc dcnslty throughout thv cnkrti WIM qiiitv i'vrii. l i r was thinkiiiu of trouble connected with tho roril' ilyrliiu of r.otton

Wl!) 100 Ib I hi* Lrctu

not glvv the samr iesults is the goods ratio was the same in both cases Y

Mr. 6. B. Adanis referred to the wiuding ot thr caki-s nnd said hr itnsiinied that thc dcnslty throughout thv cnkrti Wllb quit1 i'vrii. l i r was thinkiiiu of trouble connected with the ronl ~lwliiu of r.otton

U1 tra-violet Lamps for Fluorescence Analysis in the Textile and Related Industries

J. A. RADLEY

U1 tra-violet Lamps for Fluorescence Analysis in the Textile and Related Industries

J. A. RADLEY In the last decude inuch interest haa been aroused by

the poasibilitiee of fluoresoenae analyau for providing information, not otherwiee obtainahle, about the various procews used in many industries. I n the textile industry examination in "filtered" ultra-violet light haa become a routine procedure in mveral processes, and i t haa proved n vtaluahle auxiliary method of analysis and testing in a number of isolated caaes involving the detection of faulta in menufacture or proceseing. The various methods employed and their poseibilitioa and drawbsoks have been discussed by the preaent author nlsewherel****. Much hurni was done to the progress of the method in the early yearn following its uireption, due to extravagant c l ~ i m s msde for i t by some early workers, and even to-day this lamentable tendency manifests itself in certain books and articles in the semi-technical prom. It is, therefore, without any apology for roiteration that the warning stressad elsewhere1.*TS is repeated here, viz. that whilst "fluorescence analysis" or testing by fluorescence is an extremely valuable complementary method, the reeults should be taken in conjilnction with those obtained by other normal testing methods before an opinion is expreseed. If the reaulte obtained with the ultra-violet lamp appear to contradict those ohtained by mesne of other phyeicd ar chemical methods, i t is safer to ignore the result8 of the fluorescence ta ts than to accept them in preference to the other teste. The type of lamp or filter uaed may influence the results

obtained. so the combination used in the fluomsoenre work ehould always be described if the results are published. It is then pomible for other workers to oorrelate their own 5ndings with t h w in the publioation.

There is a demand for eamly portable ultra-violet lamps, fitted with the necessary "dark fdter", for use in following certain works prooeeses, for mobility and ada tability m the laboratory and for certain apecial types ofwork. e.g. advertiaing, display and thestri@al work. Thio demand haa been met by various A m , and the types of ap aratus available are discussed below, together with a brieFreview of the filters available for this work.

The various ultra-violet lamps on the market are products which, to be understood, require some knowledge of electric discharge I m p s in Renerd, for, owing to their ronvenienoe in urm and their npectral oharacterietics. diaoharge lamps are very widely used in Ruomcenoe work, almost to the exclueion of any other type of source of rtltm-violet radiation.

Wlthin the lest 12 yews the luniirious diechargo lamp has grown from an interesting laboratory fitting to a oommercial artiole. In such lamps the rurrent pmses through a vapour or g a s contained in a tube or bulb, thus oeuaing emiselon of light, the spectral characteristics of which am largely govnrned by the nature of tho gas in the tube. The spectral radiation from a disc-harge tube consists of 8 series of sharply tlofiried spectral lines, where- that emitted by the carbon arc, Alanient lamps and the Bun is continuous and consists of radiation due to matter a t a high temperature and known na temperature radiation. In some casea there are nuineroun linea which are BO close together that the appearance in almost t.hat of a continuow spectrum.

Discharge tubm emit energy only a t certain wuvshgths lyiog chiefly in the visible and ultra-violet regions, whereas. with Bources of temperature radiation, much energy is given out in the infra-red region. "bus, for fluorescence en~lySis, a discharge tube oonstitutm one of the most effioient murcea of ultra-violet light, in addition to itfi other advantages. The maximum efficiency possible with any temperature radiator, consistent with reaeonable life, is about !XI lumens per watt, hut, due to dissipation of energy aa heat, the effloiency of even the be& discharge lamps is only 10-25:& of that theoretically possible. Nevertheless, those lampe are much moro efflcient than temperature radiators for use in fluorescenre analysis.

A brief consideration of how the electric discharge tube works is sutllcient to explain one or two of its features which are ofton rather puzzling. When an elertron in removed from an atom, the etom is loft potlitively charged and becomes a positive ion. A few positive ionw nnd frre elaetrona are always present in the gas or vapour in ti11 electrio diecharge tube, due to the ionifling actioii of thii very penetrating coamic radiation. When a potontinl difference is applied between the two electrodes sealed into the tube, the positive ions move in one direction and tho eleotronn in the opposite direction, thus producing 811 extremely mall current. While moving towards the elmtrod@, them positive ions and electrons collide with neutral atoms and, when travelling above 8 certain minimum velooity,. the ion can transfer sufficient energy to the neutral atom to dirrplace an elertron in the neutral atom and force i t into an outer orbit. Depending on tho kind of atom involvetl, a certain miniinurn number of energy quanta are required to cause this displacement, and energy in excem of this value manifests itself RE