194 POISONS : THEIR EFFECTS AND DETECTION. [§ 24 I. 
sulphate is obtained, due to the breaking up of the compound sulphate, 
and from this second weight the amount of acid can be obtained, e.g. in 
the case of phenol—C 6 H 5 HS0 4 : BaS0 4 : : 174 : 233. 
§ 241. Assay of Disinfectants, Carbolic Acid Powders, etc.— For the assay of 
crude carbolic acid, Mr Charles Lowe 1 uses the following process :—A thousand 
parts of the sample are distilled without any special condensing arrangement; water 
first comes over, and is then followed by an oily fluid. When a hundred parts of the 
latter, as measured in a graduated tube, have been collected, the receiver is changed. 
The volume of water is read off. If the oily liquid floats on the water, it contains 
light oil of tar ; if it is heavier than the water, it is regarded as hydrated acid, con¬ 
taining 50 per cent, of real carbolic acid. The next portion consists of anhydrous 
cresylic and carbolic acids, and 625 volumes are distilled over; the remainder in the 
retort consists wholly of cresylic acid and the higher homologues. The relative propor¬ 
tions of carbolic and cresylic acids are approximately determined by taking the 
solidifying point, which should be between 15’5° and 24°, and having ascertained 
this temperature, imitating it by making mixtures of known proportions of carbolic 
and cresylic acids. 
E. Waller 2 has recommended the following process for the estimation of carbolic 
acid. It is based on the precipitation of the tar acids by bromine, and, of course, all 
phenols precipitated in this way will be returned as carbolic acid. The solutions 
necessary aie— 
1. A solution containing 10 grms. of pure carbolic acid to the litre; this serves 
as a standard solution. 
2. A solution of bromine in water. 
3. Solution of alum in dilute sulphuric acid. A litre of 10 per cent, sulphuric 
acid is shaken with alum crystals until saturated. 
The actual process is as follows :—10 grms. of the sample are weighed out and 
run into a litre flask, water added, and the mixture shaken. The flask being finally 
filled up to the neck, some of the solution is now filtered through a dry filter, and 
10 c.c. of this filtrate is placed in a 6 or 8 ounce stoppered bottle, and 30 c.c. of the 
alum solution added. In a similar bottle 10 c.c. of the standard solution of carbolic 
acid are placed, and a similar quantity of alum solution is added, as in the first bottle. 
The bromine-water is now run into the bottle containing the standard solution 
of carbolic acid from a burette, until there is no further precipitate ; the bottle is 
stoppered and shaken after every addition. Towards the end of the reaction the 
precipitate forms but slowly, and when the carbolic acid is saturated, the slight 
excess of bromine-water gives the solution a pale yellow tint. The solution from the 
sample is treated in the same way, and from the amount of bromine-water used, the 
percentage of the sample is obtained by making the usual calculations. Thus, sup¬ 
posing that 5 c.c. of the standard required 15 c.c. of the bromine-water for precipita¬ 
tion, and 10 c.c. of the solution of the sample required 17 c.c., the calculation would 
be 15x2 : 17 = 100 : x per cent. With most samples of crude carbolic acid, the pre¬ 
cipitate does not readily separate. It is then best to add a little of the precipitate 
already obtained by testing the standard solution, which rapidly clears the liquid. 
Koppeschaar’s volumetric method is more exact, but also more elaborate, 
than the one just described. Caustic normal soda is treated with bromine until 
permanently yellow, and the excess of bromine is then driven off by boiling. The 
liquid now contains 5NaBr-f-NaBr0 3 , and on adding this to a solution containing 
carbolic acid, and a sufficient quantity of hydrochloric acid to combine with the 
sodium, the following reactions occur :— 
(1) 5NaBr+NaBr0 8 +6HCl=6NaCl+6Br+3H 2 0 • 
and 
(2) C 6 H 6 0 + 6Br=C 6 H 3 Br a 04-3HBr. 
1 Allen’s Commercial Organic Analysis, vol. i. p. 311. 
2 Chem. News, April 1, 1881, p. 152. 
