Intelligence and Miscellaneous Articles. 315 



arsenic, if they be present, are precipitated ; and the precipitate con- 

 tains no sulphuret of lead. As to the iron which the sulphuric acid 

 contains, it is well known to be the protosulphate, upon which hy- 

 drosulphuric acid has no action. 



The non-formation of sulphuret of lead in this case had led the 

 author to think, contrary to the general opinion, that commercial 

 sulphuric acid does not contain sulphate of lead, and consequently 

 that this metal is completely insoluble in it ; but on trial he adopted 

 a contrary opinion. The following experiments were performed : — 



1 . Recently precipitated sulphate of lead was put into a glass and 

 covered with concentrated sulphuric acid, and exposed to the air 

 during about six months, taking care to shake the mixture occa- 

 sionally. The acid was considerably diluted by absorbing atmo- 

 spheric moisture. This acid, rendered clear by standing, was sub- 

 mitted to the action of a current of hydrosulphuric acid gas without 

 occasioning any discoloration or precipitation of sulphuret of lead. 



2. Sulphuric acid of sp. gr. about l - 540, was boiled for an hour 

 on sulphate of lead, and afterwards the experiment was repeated 

 with concentrated acid. The liquids rendered clear by standing 

 were treated with a current of hydrosulphuric acid gas, but neither 

 precipitation of sulphuret of lead nor discoloration were produced. 



These experiments seem to prove that even boiling concentrated 

 sulphuric acid does not dissolve sulphate of lead, and consequently 

 that the acid of commerce cannot contain any ; but on adding water 

 to the acids which had been boiled with the sulphate of lead, after 

 they had become clear, a considerable white precipitate was formed ; 

 this could only be attributed to the separation of the acid from the 

 sulphate of lead which it had dissolved, an effect which is precisely 

 similar to the precipitation of sulphate of barytes dissolved by con- 

 centrated sulphuric acid. 



An aqueous solution of hydrosulphuric acid was then added to the 

 acid which had been treated with water, and still holding in suspen- 

 sion the white precipitate which had been formed ; but neither the 

 liquid nor the precipitate was rendered brown by the hydrosulphuric 

 acid : they remained perfectly colourless. From these facts M. Du- 

 pasquier began to suspect that sulphuric acid prevented the forma- 

 tion of sulphuret of lead ; that this is actually the case was proved 

 by the following experiment : — 



Sulphate of lead was put into a glass and covered to about 1£ 

 inch of concentrated sulphuric acid, agitation being used to effect 

 their mixture. Being afterwards subjected to the action of hydro- 

 sulphuric acid, both in its gaseous state and in solution, the mixture 

 remained perfectly white. The same result was obtained by causing 

 hydrosulphuric acid to react upon sulphuric acid, which had been 

 boiled with sulphate of lead, and then mixed with this salt ; in 

 neither case was there the slightest formation of sulphuret of lead. 



In order to prove that the discoloration both of the dissolved and 

 undissolved sulphate of lead was owing to the presence of an excess 

 of sulphuric acid, the following experiments were performed : — 



1 . The precipitated sulphate of lead was washed with distilled 



