DISINFECTANTS, ETC. 139 



cent KOH or NaOH. Distil off spirit and evaporate to 

 about 30 c.c., and cool. If any tar oils separate out, filter 

 them off, run the filtrate into a burette, and add cautiously 

 and a little at a time, 50 per cent sulphuric acid, until the 

 alkali present is completely neutralized. The tar acids 

 are liberated, and will rise to the surface and form a separate 

 layer, the volume of which can be read off. As the sp. gr. 

 of crude carbolic acid is about 1050, the volume x 1-05 

 will give the weight, and the result x 2 gives the percentage 

 of available carbolic acid present in the powder. 



2. This method extracts all the carbolic present, and is 

 suitable for samples which contain free lime. 50 grm. 

 of the previously well-mixed powder are placed in a large 

 mortar, and a cold mixture of equal parts of sulphuric 

 acid and water (i.e., 50 per cent) is added drop by drop, 

 with constant stirring, until all the lime has been converted 

 into sulphate, and the mixture is just acid. This is 

 determined by repeated testing with litmus, removing and 

 moistening a small fragment of the powder. The process 

 must not be hurried, or heat sufficient to volatilize the 

 free phenol present will be generated (takes one hour). 

 The result is a dry powder, free from lumps. If it is 

 moist, add some calcium sulphate. Now extract with four 

 lots of ether, filtering each time the supernatant ether 

 through a small filter into 50 c.c. of 10 per cent NaOH. 

 Agitate well and distil off the ether (almost). Transfer to 

 a separator, washing out flask with small quantities of 

 water and ether, which are added to the same. Separate, 

 wash ethereal layer with water, separate again, and mix 

 with first lot. Reduce bulk by evaporation to 30 c.c., 

 transfer to a burette, and treat as in (i). 



Sodium Sulphite and Sulphurous Acid. See page 

 121. 



Zinc Chloride. Estimate gravimetrically by precipita- 

 tion with Am 2 S, filter, dry, ignite, and weigh as ZnO. 



Copper Sulphate. Precipitate as CuO \\ith NaOH. 

 Collect, dry, ignite, and weigh as CuO. 



The " Lancet " Commission appointed to inquire into 

 the Standardization of Disinfectants, issued a report, which 



