§ 235. Examination of the Urine for Phenol or Cresol.—It has been previously stated (see [p. 174]) that the urine will not contain these as such, but as compounds—viz., phenyl or cresyl sulphate of potassium. By boiling with a mineral acid, these compounds may be broken up, and the acids obtained, either by distillation or by extraction with ether. To detect very minute quantities, a large quantity of the urine should be evaporated down to a syrup, and treated with hydrochloric acid and ether. On evaporating off the ether, the residue should be distilled with dilute sulphuric acid, and this distillate then tested with bromine-water, and the tri-bromo-phenol or cresol collected, identified, and weighed.
Thudichum[215] has separated crystals of potassic phenyl-sulphate itself from the urine of patients treated endermically by carbolic acid, as follows:—
[215] Pathology of the Urine, p. 193.
The urine was evaporated to a syrup, extracted with alcohol of 90 per cent., treated with an alcoholic solution of oxalic acid as long as this produced a precipitate, and then shaken with an equal volume of ether. The mixture was next filtered, neutralised with potassic carbonate, evaporated to a small bulk, and again taken up with alcohol. Some oxalate and carbonate of potassium were separated, and, on evaporation to a syrup, crystals of potassic phenyl-sulphate were obtained. They gave to analysis 46·25 per cent. H2SO4, and 18·1 K—theory requiring 46·2 of H2SO4 and 18·4 of K. Alkaline phenyl-sulphates strike a deep purple colour with ferric chloride. To estimate the amount of phenyl-sulphate or cresol-sulphate in the urine, the normal sulphates may be separated by the addition of chloride of barium in the cold, first acidifying with hydrochloric acid. On boiling the liquid a second crop of 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—C6H5HSO4 : BaSO4 :: 174 : 233.
§ 236. Assay of Disinfectants, Carbolic Acid Powders, &c.—For the assay of crude carbolic acid, Mr. Charles Lowe[216] 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, containing 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 proportions 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.
[216] Allen’s Commercial Organic Analysis, vol. i. p. 311.