216 



THOMAS COOKSEY. 



A short VOLUMETRIC METHOD for the ESTIMA- 

 TION of SULPHURIC ACID. 



By Thomas Cooksey, ph. d.. b. sc. 



[Read before the Royal Society of N. S. Wales, December 4, 1907.'] 



This method depends upon tlie volumetric estimation of 

 the excess of barium chloride left in solution after precipit- 

 ation of the sulphuric acid as sulphate of baryta. 



Estimation of Calcium and Barium by standard solution 

 of Sodic Carbonate.— The metals of the calcium group can 

 be directly estimated by a solution of sodium carbonate, 

 provided no metals other than fixed alkalies are present. 

 A method of estimating calcium has been described which 

 consists of gradually adding the carbonate of soda to the 

 hot solution until the. pink colour given by phenol-phthalein 

 remains permanent after boiling for a few minutes. This 

 method is somewhat tedious and has the disadvantage of 

 leaving a feeling of uncertainty as to the end point of the 

 reaction. I have improved this process very considerably 

 by making use of spirit of wine to cause the rapid precipit- 

 ation of the carbonate of lime. The process is perhaps best 

 carried out as follows: — The solution containing the calcium 

 or barium salt free from carbonates, borates, phosphates, 

 and silicates is made just neutral to phenol-phthalein with 

 caustic potash. Standard sodic carbonate is now run in in 

 the cold, and occasionally small amounts of spirit of wine 

 or methylated spirit added with constant stirring until the 

 proportion of spirit in the mixture at end of titration 

 amounts to about one half of the whole. The carbonate of 

 lime or baryta is then immediately thrown down and the 

 end reaction with phenol-phthalein is sharp and distinct, 

 more especially so in the case of barium. In dilute solutions 



