DISCUSSION OF RESULTS. 



Skinner comparing the Barlow-Tollens and peroxid methods found 

 that the latter gave slightly higher results in five out of seven cases, 

 the difference averaging about -(-0.11 per cent of SO 4 or +0.036 per 

 cent of sulphur. The proposed method gives sulphur results about 

 0.1 per cent lower than the peroxid method, the average of the 12 

 values which were lower by the proposed method would thus be about 

 0.064 per cent less than by the absolute method. Both of these dis- 

 crepancies are well within the experimental error. Also it should be 

 noted that the difference between the figures obtained by fusing the 

 barium sulphate in the peroxid method and reprecipitating, and those 

 resulting from the first precipitation by the proposed method (as 

 given in columns B and C, Table 1) varies from 0.04 to -f 0.11 per 

 cent. In six out of twelve cases the figures obtained by the first pre- 

 cipitation in the proposed method are nearer the values obtained by 

 fusing and reprecipitating the barium sulphate in the peroxid method 

 than they are to the results of the first precipitation in the peroxid 

 method. The peroxid method gives a very high blank as compared 

 to the proposed method; with the former this blank amounted to 

 from 0.009 to 0*0028 per cent of sulphur and in the latter it amounts 

 to from to 0.0007 per cent. As the blanks by the peroxid method are 

 very high an error would be introduced if they were not run in each 

 set. This is very clearly demonstrated in the determinations of sul- 

 phur in sulphuric acid solutions as given in Table 2. 



SULPHURIC ACID SOLUTIONS. 



To determine the effect of the salts in solution on the precipitation 

 of sulphuric acid, fusions were made by the peroxid method and by 

 the proposed method, definite volumes of dilute sulphuric acid being 

 added to the solutions and blanks run at the same time. The fusions 

 were made exactly as in the case of the total sulphur determinations 

 given in Table 1. Then they were dissolved, an excess of 2 cc of 

 hydrochloric acid was added, the solution was filtered, and the meas- 

 ured amount of dilute sulphuric acid added. The sulphuric acid was 

 precipitated with barium chlorid solution in the same manner as in the 

 other determinations. The results are given in Table 2. 



U. S. Dept. Agr., Bureau of Chemistry Bui. 116, p. 92. 

 [Cir. 56] 



