METHOD FOR THE DETECTION OF PRESERVATIVES. 1031 



were thoroughly pulped, about 50 grams mixed with dilute phosphoric 

 acid, and the mixture allowed to stand for some time. The mixture 

 was then strained through a coarse cotton bag. The resulting liquid, 

 of which there should be about 50 to 75 cc, was then subjected to distil- 

 lation. The first 5 cc of the distillate were examined for sulphurous 

 acid. For this purpose add bromin water, boil till the yellow color 

 disappears, and add solution of barium chlorid. Any precipitate of 

 barium sulphate is of course indicative of sulphurous acid. A portion 

 of the first distillates can also be tested for hydronaphthol by Beebe's 

 method. 1 This is done by making the liquid very faintly alkaline 

 with dilute ammonia, and then as slightly acid with dilute nitric acid. 

 Next add a drop of concentrated solution of sodium nitrate. In the 

 presence of hydronaphthol, a rose color is developed. The reaction is a 

 delicate one, but the process requires much practice with known solu- 

 tions before it can be used. The test, however, is extremely charac- 

 teristic. 



After testing for sulphurous acid and hydronaphthol, the distillation 

 is allowed to proceed till the contents of the distilling flask are nearly 

 down to dryness and salicylic acid tested for in the last portions, 

 preferably in the last 10 cc. In case much is present salicylic acid 

 conies over daring the whole course of the distillation, but it is mainly 

 contained in the final portions. This tendency may be illustrated by 

 the following experiment: Twenty-five ing of salicylic acid were dis- 

 solved in 250 cc of water containing a little phosphoric acid and the 

 mixture distilled, the distillate being collected in portions of 25 cc each. 

 The first fraction gave a distinct but pale color with iron chlorid, the 

 next a somewhat stronger reaction, and the next a still more marked 

 color. In this last portion the salicylic acid amounted to about 

 0.3 nig. The next two portions gave increasingly brighter color tests, 

 the amounts of the acid contained in each being, respectively, 0.4 and 

 0.5 mg. In the sixth portion there were about 0.8 mg, and in the fol- 

 lowing fraction about 0.9 nig. The eighth portion of 25 cc contained 

 2.2 mg, and a final portion of 15 cc contained 3 mg. The amount of 

 salicylic acid in these distillates was estimated colorirnetrically. 



In detecting salicyltc acid the method of macerating the contents of 

 the can with dilute acid and distilling the resulting fluid directly works 

 very well in those cases where the quantity of the acid present is not 

 too small, but much better reactions can be obtained by drying the 

 sample of canned food, powdering, making into stiff paste with sul- 

 phuric acid, extracting with ether, evaporating the ether, taking up 

 the residue with water containing a little alkali, making acid with 

 phosphoric acid, and then distilling. In the distillate thus obtained, 

 salicylic acid can be distinguished even when existing in the original 

 substance in quantities too small to be identified by the first mentioned 

 course of procedure. 



i Analyst, 1888, 13, 52. 



