10 
manufacture of 40 per cent solutions of this compound are based on 
the methods already set forth in the above. These methods, however, 
are secret processes protected b}^ chemical patents, and hence are not 
described in the literature. 
TESTS. 
The following is an outline of the most important methods now in 
use for the detection and determination of formaldehyde. Those most 
favorabh^ mentioned in the literature are briefl}" described. 
At the present time formaldeht^de is extensively employed as an 
antiseptic, germicide, and food preservative. Methods therefore have 
been devised whereby it may be detected and determined (a) in strong 
solutions, such as formalin; (b) as a gas in the atmosphere of closed 
spaces, and (cj in admixture with various other substances, usually of 
an organic nature, such as milk and other foodstuffs. 
The following qualitative methods are said to be the most delicate 
and trustworthy: 
Hehner’s (10) and its modifications. Bring into contact without mix- 
ing two layers, the bottom one of concentrated sulphuric acid, the top 
one of milk suspected of containing formaldehyde. Richmond and 
Bosele}" (11) dilute the milk with its own volume of water, which tends 
to prevent charring. A purple color at the zone of contact indicates 
formaldeh^Me. The casein of the milk is one of the reagents. The 
test can be applied to substances other than milk by the addition to 
the liquid to be tested of formaldeh^^de-free milk or certain other pro- 
teids, the best, according to Acree (12), being a globulin extracted from 
squash seeds. Adding to the acid a solution of ferric chloride (Lyons, 
13) or solid potassium chloride (Luebert, 14) is also said to be an 
improvement. 
Lebbin’s (15). Boil a few c. c. of the liquid with 0.05 G. of resor- 
cinol and about an equal volume of 50 per cent sodium hydroxide 
solution. The ^^ellow color changes to red. 
Rimini’s (16). Directly applicable to foods, especially milk. To 
15 c. c. of the substance are added successively 1 c. c. of dilute 
phenylhydrazine h}Mrochloride solution, a few drops of fresh sodium 
nitroprusside solution, and a few drops of caustic soda solution. A 
blue color is produced, turning finall}" red. 
Hydrochloric acid test (51). Commercial h 3 Mrochloric acid (specific 
gravit}" 1.2) containing 2 c. c. of 10 per cent ferric chlorid per liter is 
used as a reagent. Add 10 c. c. of the acid reagent to an equal volume 
of milk in a porcelain casserole and heat slowh^ over the free flame 
nearl}" to boiling, holding the casserole by the handle and giving it a 
rotar}" motion while heating to break up the curd. The presence of 
formaldehyde is indicated by a violet coloration, varying in depth with 
the amount present. In the absence of formaldehyde the solution 
