18 BULLETIN 1308, U. S. DEPARTMENT OF AGRICULTURE 
10 minutes, when action has practically ceased even in presence of un- 
dissolved mercury, 35 cubic centimeters of water are added. If basic 
salt separates, dilute nitric acid is added to dissolve it. Sodium 
hydroxide, 10 per cent, is next added by drops with thorough mixing 
until the curdy precipitate following a single drop no longer redis- 
solves but disperses to an evidently permanent turbidity. Then 5 
cubic centimeters of dilute nitric acid are well mixed in. The solu- 
tion is perfectly fit for use on the day following its preparation, but 
later deteriorates. 
Standard benzophenol is prepared by dissolving a weighed 
amount of the pure substance, possessing a congealing point of not 
lower than 40° C. in water to make not less than a 1 per cent solu- 
tion. From this stock solution is made a 0.025 per cent solution of 
phenol in distilled water, which constitutes the final standard and 
which should be prepared on the day of use. Dilute formaldehyde 
solution is prepared by diluting 2 cubic centimeters of the com- 
mercial 37 per cent solution to 100 cubic centimeters with distilled 
water. 
APPARATUS 
In addition to ordinary burettes, pipettes, and flasks are required 
matched Nessler cylinders, 50 cubic centimeters, tall form, and a sup- 
ply of test tubes, about 180 by 20 millimeters, graduated at 25 cubic 
centimeters, for which a file scratch will serve, and provided with rub- 
ber stoppers; also a water bath for heating these tubes, which may 
be extemporized from a beaker containing a disk of wire gauze 
raised somewhat from the bottom. 
PROCEDURE 
In the case of a commercial cresol about 2.5 grams are weighed 
by difference into a 250 cubic centimeter volumetric flask, dissolved 
in 10 cubic centimeters of 10 per cent sodium-hydroxide solution and 
made to the mark with water. Shortly before the determination is 
to be executed 5 cubic centimeters of this solution are placed in a 200 
cubic centimeter volumetric flask, and after dilution to about 50 
cubic centimeters 1 drop of methyl-orange indicator is added and 
then dilute nitric acid until practical neutrality is reached, after 
which the solution is made to the mark and well mixed. In the case 
of a saponified cresol solution about 5 grams are taken, and are simi- 
larly diluted with water only. Of the diluted solution 5 cubic centi- 
meters are placed in each of two of the graduated test tubes, and in 
each of two others are placed 5 cubic centimeters of the standard 
phenol solution. Then 5 cubic centimeters of the Millon reagent are 
flowed down the sides of each tube, mixed in. and the tubes are 
placed in a water bath already brought to boiling and maintained 
at boiling for exactly 30 minutes. They are then immediately and 
thoroughly cooled by immersion in a bath of cold water for at least 
10 minutes, after which 5 cubic centimeters of the dilute nitric acid 
are added to each. 
After brief mixing 3 cubic centimeters of the dilute formaldehyde 
are added to one of each pair of tubes; all are made to the 25 cubic 
centimeter mark with water, stoppered, and well shaken, then put 
aside to stand overnight. The next day the tubes to which formal- 
dehyde had been added will have faded to a yellow, while the others 
