290 F W. Mar — Estimation of Barium as the Sulphate. 



ately. It can be safely filtered with or without pressure in ten 

 minutes. In one instance, iii the course of the experiments 

 just detailed, 2- grins, of barium chloride were precipitated in 

 the presence of 30 cm 3 of hydrochloric acid, the precipitate 

 was allowed to settle clear, and was then filtered and washed, 

 the whole operation being completed in seven minutes. This 

 rapid subsidence of the precipitate is seen in hot solutions only 

 — 75° C. being the lowest temperature compatible with the 

 attainment of good results, and 85° to 90° better. 



To ascertain whether small amounts of barium would be 

 precipitated in like manner from these acid solutions, a series 

 of experiments was made with solutions containing in 400 cm 3 , 

 10 cm 3 of hydrochloric acid and 5, 10, 15, 20, 25, 30 and 50 

 milligrams of barium chloride, precipitation being brought 

 about as in the experiments above. These solutions remained 

 clear a few minutes and then a very transparent precipitate 

 appeared, but in no case was it as pronounced as the more 

 finely divided precipitate produced in a neutral solution con- 

 taining 5 milligrams of barium chloride by the same amount 

 of sulphuric acid. However, by giving a circular motion to 

 the solution in the beaker, after about 20 minutes a small coni- 

 cal heap of barium sulphate was collected in each case in the 

 center of the beaker. 



Experiments were next undertaken to ascertain whether bar- 

 ium is completely thrown out of solution when precipitated 

 under the conditions related above. The barium salt used in 

 all the experiments described below, was obtained by finely 

 powdering selected crystals of barium chloride and drying by 

 pressure between blotting papers. Portions of the same sam- 

 ple were used throughout. The hydrochloric acid used was 

 the chemically pure article of commerce and had a specific 

 gravity of 1'20. The sulphuric acid used was obtained by dilut- 

 ing the pure concentrated acid with three parts of water and 

 had a specific gravity of 1*28. 



In the first series the barium salt was dissolved in about 

 400 cm 3 of water, 15 cm 3 of hydrochloric were added, and pre- 

 cipitation was brought about by adding 10 cm 3 of the dilute 

 sulphuric acid. The precipitates were filtered, after standing 

 about ten minutes, upon asbestos felts in perforated platinum 

 crucibles. 



BaCl 2 . 2H 2 taken. 



BaS0 4 found. 



Error. 



(1) 0-5002 grin. 



0-4760 grm. 



0-0016 grm.— 



(2) 0-5042 " 



0-4812 " 



0-0006 " — 



(3) 0-5038 " 



0-4786 " 



0-0025 " — 



(4) 0*5002 " 



0-4760 " 



0-0016 " — 



(5) 0-5046 " 



0-4812 " 



0-0006 " — 



(6) 0-5038 " 



0-4804 " 



0-0006 " — 



