July, 1016.1 C O R R E S P O N D E N C E - P A C K DYEING M A C H I N E S . 187

brown under any of the above treatments. Presumably this is due to salt forniat,ion bet>ween the amido compounds of wool and t'lie .acid {Fort and Lloyd: this JoztrnaZ, 1914, 1). 5 ) , and may be compared to the behaviour of certain well-known amido compounds, e.g., phenylene diamines, which in a quite pure state are white, but usually are liable to develop a, brownish colour, e.g., on keeping or under similar treatments to t'hose above discussed for wool. These amido compounds likewise keep their colour better in the form of s a h , and a very brown specimen of base will usually improve in colour considerably by converting i t into a salt or acidifyirig its aqueous solution. The effect of dkalis on many dianiines and amido-naphthols is to promote browiiiiig a t a rapid rate. (4) Stoving amppears to embrace two functions, firstly that of an acid, and secondly an exttra degree of whiteness is conferred by reduction or some special action of sulphurous acid. The extra effect thus gained is not per- manent in the case of exposure. It iR found that this extra bleached effect, is also rapidly removed by boiling stoved wool with sulphuric acid (say 5 per cent.), and in fact it is not imparted to the same extent by stovirig if the wool has previously been boiled with sulphriric acid. It seems probable therefore that' the effect of stoving is mainly on the ainido groups, and the brown basic degradation products of wool formed from its free arnido compounds. ( 5 ) A brown colour may be iinpart,ecl to wool by treatments other than those named. The effect of sulphuric, hydrochloric, phosphoric, mid sulphurous acids a t high concentrations, in the cold, is especially interesting in developing a, brown colour which disappears on dilution. The loss of SO, from wool in the treatment' with the first three of these acids must be rega,rtled as incidental and unimportant' in production of the brown colour, since something similar occurs also when a,ii excess. of sulphurous acid in used. In such cases air oxidatmion is excluded from the possible causes of browning, which reseinbles the colour reactions of certain colourless oxygen and sulphur compounds investigated by Raeyer in connection with tJhe halochronie theory. (6) While the action of heat can cause the brown- ing of wool in a non-oxidising atmosphere such as coal gas, browning occurs to a much greater extent when air is present during heat)ing. There is no doubt that wool will go brown 011 heatting, sbeaming, boiling, or alkali treatment,, apart from the action of air, but i t seems oer- tain t,hat when air is present it, tends to increase the brown colour by promot'ing oxidat,ion to a greater extent than ca,n internal reactions a,lone. (7) A number of experiments on pure silk lend additional support to the conclusions drawn in the case of wool. Silk is a much less basic fibre than wool, and treatments which affect the development of amido groups or depend upon the acbivjty of free amido groups, exert less influence on silk than wool. Quite in accordance with this are the observations that fading affects

the affinity for dyestuffs less in the case of silk than wool. Silk is less liable to turn brown on heating or hot-ironing than wool (on ironing i t was found that a temperature at least 50" C. higher was required for silk to obtain an effect sirnilar to that with wool). Acid treatment, before or after ironing, irnproves the final colour, but is not so effective as in the case of wool a t a similar temperature of heating or ironing. Strong acids, including H,S0,, cause a brownish colour on silk, removed by washing. Steaming also causes browning, partly affected by acid treatment. as in the case of wool, but not nearly to the same extent. (8) After reaching the above conclusions inquiry was made as to the ex- perience of the trade on certain important points. The author here records his obligation to Harry Hey, Esq., for the following confirmatory reply :-" Wool showb ' fades ' on re-dyeing more than silk. The former preparation or finish of the material before exposure has a great effect also. The fade marks are usually very bad on material which has been boiled or steamed to get a lustre or spot-proof finish."

Technical College, Bradford.

Gorreeyoiibeiice. Pack Dyeing Machines.

To the Editors of the Journal of the Society o j Dyers and Colourists.

Sirs,-On page 133 in the May issue of your Journal t2he following statement appears as part of the lecture given by Mr. F. Smith on " Pack Dyeing Machines " :-

" Since tjhe war commenced it, has been diffic$t,, and in many cases inipossible, to get level result's with the sulphide colours now made."

We must ask you to allow us to publish an emphatic contradiction of this statenieiit as far as relates to the sulphur colours being marketed by British Dyes, Ltd., viz., Cross Dye Blacks, Cross Dye Brown, Cross Dye Yellow, Cross Dye Drab. Two members of our dyeing staff have had experience on the large scale with the above sulphur colours, and have got perfect results. In one case one ton of loose cotton was dyed in a machine "System Coloss" with Cross Dye Black, arid a perfect result was obt,ained. . In other cases, compound shades of Yellow, Brown, and Black were dyed in a pack machine which held 180 t,o 200 lbs. of cotton, according to the nature of the cot,ton. Perfectly level results were obt,ained in this case also.

If desired we are prepared to place before Mr. Smith patterns of t.hese results, and also to give him the names of the firms a t which these dyeings were made.

We are, &c., For BRITISH DYES, LIMITED,

Hucldersfielcl, C. M. WHITTAKER. May 24th, 1916.