OP ARTS AND SCIENCES. 23 



on the other hand, it is impossible to obtain any satisfactory control 

 either over the chloride of antimony which escapes or the oxide which 

 is left behind. Unfortunately, in starting from metallic antimony, we 

 cannot avoid a large excess of hydrochloric acid in the solution, and 

 must therefore expect more or less oxichloride of antimony in the pre- 

 cipitate. Assuming therefore that 15 cubic centimetres of strong hydro- 

 chloric acid were taken to dissolve every gramme of antimony, which 

 was as little as could conveniently be used (but from this the greater part 

 of the HCl gas was expelled during the subsequent boiling), it became, 

 in the second place, an object to determine how much tartaric acid was 

 required to hold the antimony in solution, and to I'educe to a minimum 

 the occlusion of oxichloride of antimony by the precipitated sulphide. 

 With this view the following experiments were made. Four solutions 

 were prepared by dissolving in each case 2 grammes of antimony in 30 

 cubic centimetres of hydrochloric acid, and reducing the solution as 

 above described. To the first of these were added 5 grammes of tartaric 

 acid, to the second 7 grammes, to the third 10 grammes, and to the 

 fourth 20 grammes. They were then each diluted with water to one 

 litre. In the first, oxichloride of antimony was precipitated at once. 

 The other three remained clear; but, in the second and third, crystals of 

 oxichloride formed on standing over night, and in the inverse propor- 

 tion to the amount of tartaric acid added. On subsequently heating to 

 boiling, the same crystals were precipitated even in the last, and the 

 amount in the others very greatly increased. This crystalline precipi- 

 tate formed as the solution was heated, and was deposited like acid tar- 

 trate of potassium wherever the glass rod touched the sides of the flask. 

 From the first and second solutions almost the whole of the antimony 

 was thus separated. 



These crystals were analyzed, and found to be the oxichloride 

 Sb^O^Clo. They will be described in a future paper. It is evident 

 from these experiments that, under the conditions we have given,* 

 from 5 to 10 grammes of tartaric acid to each gramme of antimony 

 are required to prevent the formation of oxichloride of antimony, even 

 in a cold solution ; and our experience shows that, even with the larger 

 amount, a perceptible although very small quantity of oxichloride is 

 occluded by the precipitate formed with hydric sulphide. Moreover, 



* In solutions of the same strength which have not been perfectly reduced, 

 although containing but little of the higher chloride, the oxichloride does not 

 appear to form nearly so readily ; but we have made no quantitative experiments 

 on this point. 



