REPORT OF CHEMICAL LABORATORY 



Application 

 of the test in 

 cases of 

 suspected 

 poisoning 



Addition of 

 latex to nati\'e 

 beer is easily 

 detected by 

 the reagent 



been established. It is not removed from its solution by ether, chloroform, or petrolenni- 



ether, but is completely precipitated by basic lead acetate in the presence of ammonia, 



the lead salt being soluble in excess of lead acetate.' Neutral lead acetate, in the 



presence of acetic acid, does not precipitate the substance, nor does basic lead acetate 



when added to a solution faintly acid with acetic acid (the free acetic acid is, of course, 



neutralised by a portion of the basic lead acetate). After reduction with zinc and 



sulphuric acid, its solution gives no coloration with sulphuric acid ; on reoxidation, 



the blue colour is produced. The substance may be removed from its solution by boiling 



with animal charcoal, and is dialysable. 



As regards the application of the test to cases of suspected poisoning, it is, of course, 



essential that a solution of the latex free from substances which would give colorations 



with the reagent, and so obscure the reaction, be obtained. Several experiments have 



been carried out, which have led to the adoption of the following method. The 



stomach contents, and, where emesis has occurred, the vomit, are digested in water 



slightly acidulated with acetic acid. To the strained liquid is added slight excess 



of neutral lead acetate, to precipitate albuminous matter, and the liquid filtered. 



The filtrate is carefully treated with basic lead acetate until no further precipitation 



results, and, after filtration, the liquid is made distinctly animoniacal. Tlie resultant 



precipitate is filtered off, carefully washed, and decomposed with dilute sulphuric acid. 



The liquid is filtered from lead sulphate, and the reagent applied to the filtrate, which 



may be concentrated if necessary. 



Experiments have shown that, by following this method, 0-5 c.c. of the latex may 



be readily detected when mixed with stomach contents. In most cases it will be found 



that the treatment with basic lead acetate and ammonia may be omitted, and the reagent 



applied direct to the filtrate from the neutral lead acetate, after freeing it from lead by the 



addition of dilute sulphuric acid. In cases where the volume of liquid to be tested is 



considerable, the treatment with ammoniacal basic lead acetate is advisable, since 



concentration of the liquid is thereby rendered unnecessary, the resultant precipitate being 



decomposed by the addition of a small volume of dilute sulphuric acid. The addition of the 



latex to merissa (the native beer made from millet) is easily demonstrated by applying 



the reagent direct to the filtered liquid. Should the latter be coloured, the preliminary 



treatment with lead acetate, indicated above, would be necessary. 



Latex, which has been thoroughly dried by exposure in an open vessel, is found 



to respond to the test after digestion with water. The concentration of dilute latex 



solutions by boiling does not affect the production of the lilue colour by the reagent, 



nor does digestion of the latex with pepsin and dilute hydrochloric acid. 



The action of the stomach juices on the latex being of primary importance as regards 



the value of the test in cases of suspected poisoning, the following experiment was carried 



out. An artificial gastric juice was prepared by digesting the fresh stomach of a sheep in 



water, and adding to the strained liquid sufficient hydrochloric acid to give it an acidity of 



0-2 per cent, hydrochloric acid. To 100 c.c. of this liquid was added 10 c.c. latex, and the 



liquid incubated at 37' C. Portions of 2.5 c.c. each were removed at intervals of 24 hours 



and the test aiiplied. The treatment with lead acetate, etc., previously described, was 



employed, a control test being applied to the gastric juice itself. From the liquid, to 



which latex had been added, positive reactions were obtained in each case, wliile the 



gastric juice itself gave no coloration with the reagent. 



1 When this lead compound [(d.) Table A, seq.] is decomposed by sulphuretted hydrogen or dilute sulphuric 

 acid, a strong solution of the colourable substance of the latex, to which test reagents may be advantageously 

 applied, is obtained. 



