90 BEPORT OF CHEMICAL LABORATOnY 



found to give the best results consists of a niixturi! of 75 c.c. concentrated sulpliuric acid 

 and 25 c.c. water, to which is added a drop of 40 per cent, formaldehyde solution. When 

 .\ confirmatory this reagent is added (not too carefully, so as to allow slight mixing) to the coagulated latex, 

 '^^' or to the decomposed ammoniacal basic lead acetate precipitate [(d) Table A], a grass-green 



I'iiig or band is dc^veloped. Almost iinmcdiatuly a strawberry-pink band begins to form 

 below the green, gradually deepening, and, after allowing to stand for a short time, 

 super-imposed bands of colour are seen in tlie following order, from below upwards : pale 

 strawberry-pink, (Uu^p strawberry-pink, purph^ (nai'i'ow ring), gi'ass-gre(Mi, chrome-yellow. 

 On now cooling in ice, and carefully shaking, a brigiit olive-green solution, of decided 

 depth and permanence of colour, is obtained. 



This reagent has been applied to the four foodstuff's, which give colorations with the 

 suli)hnric acid reagent simulating in some degree the blue colour given by the latex. Both 

 strong water extracts, and similar extracts treated with lead acetate, etc. [vide Table \ 

 seq.) were tested, and in no single case was any coloration produced. The formalin- 

 sulphuric acid reagent thus furnishes a certain means of distinguishing tlio latex from these 

 foodstuffs, and of detecting it in their presence. 



The application of this reagent as a test is being extended to other foodstuffs. 



The solution of the colour-yielding substance of the latex obtained by decomjiosing 

 the ammoniacal basic lead acetate precipitate with sulphuric acid (vidp. footnote, page 88) has 

 also been submitted to the action of reagents in the following manner. After making 

 faintly alkaline with ammonia, small portions were evaporated on crucible lids to dryness. 

 To the dried residues were added a number of the customary colour i-eagents ; the most 

 striking colour reactions obtained are given below. 



(a) Sulphuric acid : — yellow, changing to orange and finally to rose-pink. 



(6) Frohde's reagent : — bright greenish-blue, changing at once to grass-green, then 

 slowly to mahogany-brown and finally olive-green. 



(c) Sulphuric acid and ferric chloride : — electric blue, changing at once to green then 



brown and finally dark olive-green. 



(d) Sulphuric acid and trace of formalin: — purplish, then rose-pink. 



Speaking generally, sulphuric acid with oxidising agents gives blue and green colours, 

 while, with reducing agents, sulphuric acid develops yellow and pink colorations. 

 Analysis of The latex of G. procera is distinctly acid in reaction ; the acidity to phenol-phthalein 



the latex ^j eight samples, expressed in terms of acetic acid, was found to vary from 0-13 grannne 



to 0-23 gramme per 100 c.c. One sample, collected from several plants, showed an 

 acidity of 0-46 per cent. These differences are probably due to the age of the plants. 

 Steam distillation of the latex showed this acidity to be fixed. 



A sample of latex, collectod from several )ilants, gave the following figures on 

 analysis : — 



Algidity, as lU'ctlt; ncid O'l.'i trnnniiic ])rr liio c.i'. 



Total solid matter 13-0 \>rr cont. 



Ash ... ... ... ... ... ... ... 2'4 pur cent. 



The ash consisted chi(^fly of magnesium, calcium, sulphates, and phosphates, and was 

 distinctly alkaline. The magnesium was present in far larger quantity than the calcium. 



Exhaustion of the latex, by Adam's fat-extraction method, with alcohol, petroleum- 

 ether, and acetone in succession, yielded a considerable extract to the alcohol, and 

 comparatively little to petroleum-ether and acetone. Tlic petroleum-ether extract 

 was varnish-like, almost colourless, and acrid in taste. The alcoholic extract was only 



