CREAM 67 



distillation ceases. The water in the U-tube is 

 mixed with 2 c.c. of Schifif's reagent. If formic 

 acid was present, the mixture will become violet 

 within a half hour. 



Schifif's reagent is obtained by dissolving i 

 gram of rosanilin hydrochlorid in 10 c.c. of 

 water, adding a mixture of 2 c.c. saturated 

 solution of sodium acid sulfite and 0.5 c.c. strong 

 hydrochloric acid, then water to make 100 c.c. 

 The solution keeps for some time in the dark. 



Agar. — This is now often used as a thicken- 

 ing agent. Although characteristic diatoms are 

 found in it, the detection of the substance by 

 isolation of these has not been practically 

 successful. Revis and Bolton recommend the 

 following method. 



50 grams of the sample are diluted with 100 

 c.c. of water, heated in boiling water and cleared 

 with 5 c.c. of 10% calcium chlorid solution. 

 The mixture is filtered, preferably in a hot-water 

 funnel, cooled and mixed with about two-thirds 

 its volume of strong alcohol. The precipitate 

 (containing any agar that may have been in the 

 sample) is separated, and boiled with 5 c.c. of 

 water until dissolved. If it contains agar, the 

 solution will gelatinize on cooling. To detect 

 the presence of gelatin in association with agar, 

 the procedure is the same, except that when the 

 precipitate is dissolved, a few c.c. of the solution 



