Notes on the Indentification of Fibres of Animal and Vegetable Origin
Post on 03-Oct-2016
78 DREAPER-" IDEN'I'lFICA1'ION O F ANIMAL AND VEGETABLE FIBRES." t 1 U t ~ ~ l 1 , IDlS.
simple apparntus designed for tleterinining departures from normal
Concerning Mr. Dreaper's remarks that the proportions of violet and orange in Logwood extract would not give a figure of value when the dye was used with a mordant for black, that depended on whether the colour of the Logwood solution influenced the character of the black.
Hc agreed with Mr. Ritchie that the con- sitlrratiou of a coininon standard of 'colour was well worth the attention of the Society, and woriltl further urge the necessity of making colour study a subject of education A list of the industries where expertness in colour judging is of intrinsic value would be intercvting.
Notes on the lndentification of Fibres of Animal and Vegetable Origin.
By W. P. DREAPER, F.I.C. Ddection of Silk, Cotton, and Wool Fibres in
Admixture.-The need for a rapid method of detecting orclinary fibres in admixture is the excuse for suggesting a test which, although simple in itself, may give, in conjunction with other tests, satisfactory results in cases where actual and definite proof as to the com- position of a fabric or the fibres it contains is necessary.
In Leconipte's test, the fibre or fabric is treated with an acid solution of nitrous acid in the dark, washed. and then introduced into an alkaline solution of P-naphthol, to which lead acetate has been added. Under these con- ditions wool is coloured black, silk is dyed to deep red, and cotton remains colourless. The disadvantage of this test is obvious in the fact that it is partly conducted in the dark. In the proposed test, only one solution is
required, and thiR may be prepared in the following manner :-
Two grins. of lead acetate are dissolved in 50 cc of distilled water, i t i d to this is added 2 grins. of sodium hydroxide, dis~olved in 30 cc. of water. The solution hoiled until clear, and 0.3 grins of Magenta, dissolved in 5 cc. of alcohol, is added, after the solution is cooled to about 60". The solution is colourless Two grins of Picric Acid may take the place of the Magenta, and the solution is made up in either case to 100 cc. and filtered if necessary. h portion of the fabric or yarn is heated for two minutc~s in this solution to somewhere near thc boiling point. In the case of Magenta, it is then washed and placed in a dilute solution of acetic or formic acid, and it is suffi- cient in this case to heat the solution t c 70"('. If, after drying, the fibre be examined uiitler the inicroscope or otherwise, any silk present will be coloured red in the case oi Magenta, or yellow when Picric Acid is used, woo will be black or dark brown, and artificial silk cotton, or other vegetable fibres whitc. A soh. tion of litharge (PbO) in sodium hydroxide maj take the place of the lead acetate. In that cast
! grms of NaHO are boiled with excess of lith- xge (5 grins.) in 50 cc. of water for 16 miniites ; 1.3 grms. Magenta, dissolved in 5 co. alcohol, ,dded after cooling, and the whole filtered and nade u p to 100 cc. with water.
Artificial silk (even where the individual ilarnents as seen under the microscope approxini- he in size to real silk) may be readily detected. ,nd these or any vegetable fibres present may be letected by their absence of colour. and the ibres may be isolated from the yarn for further rxamination.
A statement was made in the last annual meport of the German Iniperial Testing House, ,hat samples of fabrics have been received for :xamination containing artificial ancl real silk n admixture, where the two fibres were actually ipun together into a composite thread, with iubsequent weaving. According to the above iuthority, it was practically impossible in such mes for an expert to identify by sight, or handle, ,he presence of artificial fibres in the finished abric. I can confirm this statement as the wult of some trials made some time ago. k t h e r developments in this direction will be vatched with general interest.
It is also obvious that in a coinposite thread if this nature, the ordinary " burning test " will no longer apply in such investigations.
Mixtures of Silk and Wool.-To definitely dentify the preseiwe of silk in admixtitre in a lam containing superior qualities of wool [ have, as a confirmatory test, used the follow- ng method with advantage :-
A short length of yarn is placed untler the nicroscope on an ordinary glass slide ancl is oosely covered with a glass cover (circle). While it is under inspection, a drop of :oncentrated sulphuric acid is taken up on the :nd of a glass rod, and gently dropped on the slide, so that it also touches the outer rim of tho glass cover. By capillary action the sulphuric acid will pass between the glass cover and slide until it comes in contact with the fibre, and then run along the same for a certain distance.
Under these conditions and within two minutes from contact with the acid, the silk Bbre in the length of fibre which is seen to be so treated, will coinpletcly dissolve, leaving any wool present, intact. and with a little practice a rough and preliminary estimate as to the relative proportion of silk and wool present may be obtainecl.
Modification of Amino Acid I'est.--I have found the following modified form of Lecompte test useful under certain conditions, and would therefore bring it to your notice.
In this manner the time takeii for this test may be reduced from two or three hours to a few minutes, and at the same time it may be conducted in daylight or gaslight. About 0.5 grins. of sodium nitrite is dissolved in 10 cc. of water, and a few drops of colic. hydrochloric acid added. The fibre is introducecl into this solution and boilccl for two minutes. Contrary to what one might expect if this
March, 1913.1 PETRIE-A CHAT ABOUT COLOUR. 79
treatment actually leads to the formation of t diazo compound, this process can satisfactorilj replace the two hours immersion in a weakei solution in the dark a t ordinary temperatures The fibre is then removed from the solution and introduced into an alkaline P-naphtho solution, which is also brought to the boil Under these conditions ordinary silk takes E dark red colour, and Tussah or wild silk a dark chocolate brown shade. Vegetable fibres, oj course, remain colourless. This test rapidlj differentiates unbleached Tussah from ordinarj silk by chemical means. It may also be noticec that Millons reagent gives a chocolate witk unbleached Tussah, and not a red, as in thf case of ordinary silk.
Recognition of Tuwah Silk.-The published tests which distinguish ordinary silk (bombya mori) from Tussah cannot, under certain con ditions, be considered as altogether satisfactory but I would place reliance on the results ob- tained in the following general examination These tests apply to ordinary bleached Tussah as well as unbleached.
Microscopical appearance of the fibre aa com- pared with ordinary silk.
Millon reaction which gives a chocolate brow11 colour with Tussah, instead of red with ordinary silk.
Amino Acid Test, which gives a deep brown with Tussah, in place of bright red with ordinary silk.
8oluhility in Nitric Acid (cone.).-Tussah silk, us present in a fabric (degunimed), dissolves a t the boil in 30 seconds, and gives a darker colour to the solution than ordinary silk.
Insolubility in Hydrochloric dcid (conc.) or 6% NaHO Solution.-Ordinary silk completely dis- solves in each caw a t the boil in five minutes. Tussah silk does not dissolve: but the filamenk become very transparent as compared with cotton, which latter fibre may actually powder down in the acid solution.
DISCUSSION. Dr. E. Feilmann congratulated Mr. Dreaper
on the method he had found for detecting silk, cotton, and wool fibres in admixture. Quanti- tative tests on the amount of ash, especially when the fabrics were weighted, were laboriouv to carry out, and it was often difficult to draw conclusions therefrom as to what fibres were actually present. M i . Dreapers test was simple to perform, and the results obtained by it were much more certain. He would like to make the suggestion that the method be extended to include wood fibre as well as the three fibres given.
In reply, Mr. Dreaper said that the suggestion with regard to wood fibre was being worked upon. It must be remembered in this respect that artificial silk made from wood fibre did not give the ordinary wood fibre reaction. The new test must, of course, be considered in conjunction with others.
Dr. E. Feilmann proposed, and Mr. Carter seconded, a hearty vote of thanks to Mr. Lovi- bond and Mr. Dreaper for their papers.
SCOTTISH SECTION. -- A meeting was held in the Technical College,
Glasgow, on 21st December, Mr. WM. B. JACKSON in the chair.
A Chat about Colour. By W. M. PETRIE.
The mechanical limitations of dyeing and printing are perfectly well understood by every- one engaged in the daily routine of work, while the chemistry of colour is being studied by expertR, who bring the best scientific training to bear on that subject. The artistic use of colour, however, is not yet on the same sound basis, and is too much a t the mercy of quite untrained persons. The carefully studied schemes of the designer are often altered at the slighest whim of a salesman or buyer.
Elaborate experiments have been made with the object of determining upon scientific grounds the reasons for the relative agreeable- ness or disagreeablenesa of colours, but little headway had been made, as although a certain unanimity of opinion exists as to the beauty of certain tints when single and isolated, the influence of combination introduces great difficulties. The same colour can be made agreeable or the reveme, according to its sur- rounding colours, the truth being that any decorative arrangement depends for its beauty ilnd effectiveness on the adjustment of its con- trasts and harmonies, and the more eubtle thew %re the less likely ia any individual tint to be particuarly valuable if used as an isolated unit.
The study of colour is intensely interesting from two points of view ; one, the study of de- :omposed light, and the other, with which they were more directly concerned, might be called the study of pigmentary colour, embracing all dyeing, staining, and painting, and a first necessity was a broad and general scheme under which the simplest and most obvious effects of my colour upon another could be grasped, and ;he more subtle relations traced out afterwards. For the sake of simplicity, all colours could be grouped under six names-red, blue, yellow, purple, green, and orange ; these gradated from ;he normal strength upwards to white and iownwards to black, gave a simplified table iuficient for practical experiment.
Numerous diagrams were shown to illustrate ;be relations of these coloura and their 5ffects upon one another-the enhancement )r deterioration of a given colour under Xifferent combinations, and the laws which ;overned the apparent changes were ex- dained and illustrated. Some general rules governing the relations of value, i.e., light and