OF ARTS AND SCIENCES. 25 



are far smaller with the red sulphide than with the gray, which shows 

 conclusively that additional causes of error must have affected the last 

 weights, — another circumstance which sustains our judgment. 



In the first twelve determinations we did not estimate the amount of 

 the carbonaceous residue, which is assumed to be balanced by the loss 

 of chloride of antimony, although we always tested the purity of the 

 sulphide of antimony by dissolving it in hydrochloric acid, as described. 

 In determination numbered 13, by some chance concurrence of favor- 

 able conditions, we succeeded in precipitating the antimony without the 

 usual occlusion of oxichloride, although we used a large excess of hydro- 

 chloric as well as of tartaric acid. In this case, there was no evidence 

 of sublimation nor loss during conversion, but a proportionally large car- 

 bonaceous residue, which was deducted from the weight of the sulphide ; 

 and the result of this determination, as will be seen, still further corrob- 

 orates our conclusion. The same is true of some analyses of chloride of 

 antimony made more recently, in which we dissolved crystallized chloride 

 of antimony in a concentrated aqueous solution of tartaric acid, without 

 using any excess of hydrochloric acid. In these cases also, the drying of 

 the precipitate, and the conversion from the red to the gray modification, 

 were attended with no appearance of sublimation. Were we to repeat 

 the investigation with our present knowledge, we should follow the indi- 

 cations of these last analyses ; and instead of attempting to make the two 

 chief errors as small as possible, and balance them, we should seek to 

 remove from the solution all the free hydrochloric acid, and thus eliminate 

 the error due to the occlusion of oxichloride,* It would then, of course, 

 be necessary to determine in all cases the carbonaceous residue, which 

 might however be very large, without impairing the accuracy of the 

 result. Still, our experience with these antimony determinations would 

 lead us to fear that we might thus raise up as many hindrances as we 

 avoided, and the determination we have given as No. 13 is sufficient 

 for all purposes of comparison. 



Before giving the results, it only remains to describe the manner 

 in which the precipitates were dried, tested, and weighed. After that, 

 by the method of reverse filtering, the precipitate had been washed, 

 and collected in a large platinum crucible, as described on pages 14 

 and 15 of this article, it was dried in an air bath, at a temperature 



* Our experiments also indicate that, even in presence of a large excess of 

 hydrochloric acid, the occlusion of oxicliloride can be prevented by using a very 

 large excess of tartaric acid. It was under these conditions that the determina- 

 tion No. 13 was made. Of course, the occlusion of tartaric acid is then large ; 

 but, as shown, this need not impair the accuracy of the result. 



