OF ARTS AND SCIENCES. 29 



tartaric acid and diluted with water, was filtered, and the residue 

 collected on one of the smallest paper disks used in the process of 

 reverse filtering. The disk was then dried and revveighed. The con- 

 stancy of weight with these paper disks was very remarkable ; and it 

 may give greater confidence in the accuracy of our method to add 

 here a few comparisons of the weights of the larger-sized disks which 

 were used in collecting the sulphide of antimony itself, taken before 

 and after they had been used. The first column gives the original 

 weight of the disks, which were first dried at 120", and then kept 

 in an atmosphere dried by sulphuric acid. The second column gives 

 the weight of the same after it had been used in filtei-ing, and taken 

 from the crucible after the first weighing with some of the dried 

 precipitate adhering. We have only one weight of this kind re- 

 corded ; but this will show how little of the precipitate adheres to the 

 filter. The third column gives the weight of the same paper disk, 

 after washing first with sulphide of ammonium, then with water, and 

 drying. 



I. II. ni. 



Experiment 1 0.0654 gram. 0.0686 gram. 0.0654 gram. 



„ 2 0.0375 „ 0.0377 „ 



3 0.0457 „ 0.0458 „ 



„ 4 0.0436 „ 0.0437 „ 



It should here be noted that iu regarding all the carbonaceous 

 residue as extraneous matter, and subtracting its weight from the total 

 weight of the precipitate, we leave all the causes of loss in our deter- 

 minations unbalanced. We estimate as sulphide of antimony the ma- 

 terial which bears a temperature of 300" unchanged, and dissolves in 

 hydrochloric acid ; and every known cause of error must tend to dimin- 

 ish the weight obtained.* But less sulphide of antimony corresponds 

 to a higher apparent atomic weight of antimony ; and hence, in those 

 determinations in which the weight of the insoluble residue has been 

 taken into account, the tendency of all the known errors must be to 



* Besides the causes of loss we have mentioned, and the small mechanical 

 losses incident to every process of the kind, we must not overlook the fact that 

 under most conditions a precipitate of sulphide of antimony is slightly soluble 

 in the surrounding menstruum, and in our determinations this was frequently 

 indicated by a barely visible coloration of the filtrate. Moreover, in several 

 instances, we observed in this filtrate a condition which is familiar in titrations 

 of silver ; namely, a state in which either a solution of antimony or a solution 

 of hydric sulphide would strike a red coloration. 



