CREAM 67 
distillation ceases. The water in the U-tube is 
mixed with 2 c.c. of Schiff’s reagent. If formic 
acid was present, the mixture will become violet 
within a half hour. 
Schiff’s reagent is obtained by dissolving 1 
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 
