116 WILKINSON & TYLER-“VOLUMETRIC ANALYSIS OF MALACHITE GREEN” [ A p r i l 1927

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RESEARCH WORK An exhibition, illustrating the hearing of

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E X ~ I ~ I T I O ~ OF SCJENTlFIc AND hACTIC-4L

Volumetric Analysis of Malachite Green with Titanour Sulphate and Titanour

Chloride Solutions H. WILKINSON A.I.C. and

A. G. TYLER B.Sc. In a series of experiments upon the relative

stability of titanous chloride and titanous sulphate solutions, and their suitability for the titration of dyestuff solutions, we noted some differences in their behaviour towards solutions of certain dyestuffs of the Malachite Green series.

Knecht and Hibbert (“New Reduction Methods in Volumetric Analysis,” 2nd edition, p. 107, this J a r . , 1905,21,293), point out that Malachite Green acts in an abnormal manner towards solutions of titanous chloride prepared according to the methods they recommend. After the addition of a few C.C. of the reagent, the solution is decolorised, but the colour returns again in a few moments, disappearing and returning with each addition of the solution until the end-point is reached, when the colour no longer reappears.

This peculiar behaviour makes the examina- tion of such compounds more tedious, as towards the end of the reaction, decolorisa- tion occurs with very small additions of the reagent, and the colour return is slow.

When titrated against titanous sulphate solution, prepared as described in the preceding paper, it was found that a solution of Malachite Green behaved quite normally ; decolorisation only occurring on reaching the end-point .

A series of parallel titrations was made with titanous chloride and titanous sulphate, each solution being stored under an atmosphere of hydrogen and the titrations conducted in the presence of carbon dioxide. The behaviour of a number of dyestuffs of the Malachite Green series is shown in the next column.

It would seem that the ratio of Rochelle salt to colour is important when titrating with t,he sulphate. Thus, when titrating Malachite Green base, dissolved in dilute hydrochloric acid, in the presence of 50 C.C. of Rochelle salt solution (20%), with a strong solution of titanous sulphate, the dyestuff solution was decolorised, and the colour returned. Using a dilute solu- tion of titanous sulphate in 4Nlsulphuric acid, no end-point was obtained due to the large

sington, and was opened on 1st March by the Earl of Balfour K.G., O.M. The exhibition,

been most carefully arranged, and covers the whole range of operation from the raw wool to the dyed and finished fabric.

The exhibition will interest the general public as well as those engaged in the manufacture of textile fabrics.

remain ‘pen the end Of May, has

amount of acid present, but with addition of 100 C.C. of Rochelle salt solution the titration was normal, with decolorisation at the end-point.

I BEHAVIOUR DURING TITRATION WITH

DYESTUFF 1 Titanous Chloride - 1-Ma1 a c h i t e

Green cryst.. A conc. (R.D.C.) (Oxalate)

(Colour Index 667

2-M a 1 a c h i t e Green 88,708 (B.D.C.) (Double Zinc Chloride)

(Colour Index 667

3-M a 1 a c h i t e Green Base (B.D.C.) dis- solved in di- lu te hydro- chloric acid

(Colour Index 667

&Fast Green J.J.O. (S.C.I.) (Sulphate)

(Colwr Index 662

LSetoglaucine

(Colour Index 66I (GY.1

D e c o l o r i s e d , colour returns after adding a few C.C.

D e c o l o r i s e d and colour returns; but this does not occur until t,he dye IS about half reduced.

D e c o l o r i s e d with a few c.c., but col- our returns, u n t i l e n d - p o i n t i s reached.

Decolorised with a few drops. and colour returns until end-point is reached.

Decolorised with 1 c.c., but colour returns until end- p o i n t i s reached.

Gradually de- colorised.

Pit.nnous Yulphate

Gradually de- c o l o r i s e d , giving a very sharp end- point.

Gradually de- colorised un- til within a few drops from the end- point, when colour dis- a p p e a r s sharply and returns slight- ly.

Gradually de- c o l o r i s e d , colour returns slightly near the end-point .

n

Behaves as with the rhloride.

Gradually de- colorised.

Gradually de- colorised.

______ rities in behaviour raise 11

number of interesting problems, which arc reserved for discussion on another occasion.

We are indebted to the Brit,ish Dyestuff8 Corporation Ltd. for a number of specimens of dyestuffs of known constitution for analysis.

Dyeing Department, The Technical College, Huddcrefic:lcl.