Sa On the Cause of Chemical Proportions. [FeS. 



found that, though the ammonia was perfectly saturated, it was dis- 

 engaged by coQtinuing the heat while at the same time small white 

 crystals were deposited on the sides of the vessel, 1 found that 

 these were crystals of arsenious acid quite free from ammonia. 

 Hence it follows that the ammonia was completely saturated. This 

 solution well corked was exposed fi>r several days to the freezing 

 temperature of water to get rid of the arsenious acid held in solu- 

 tion by the water. The neutral ammoniacal solution was then 

 employed to precipitate a solution of 10 parts of nitrate of lead. 

 The mixture when heated deposited a white heavy matter, which 

 being washed and fused in a glass retort weighed 12-27 parts. It 

 produced a transparent somewhat yellowish glass. The resi- 

 dual liquor being treated with sulpJiate of ammonia deposited 

 0-357 part of sulphate of lead, equivalent to 0262 of oxide of 

 lead. We must subtract these 0262 from the 6-731 contained in 

 the nitrate of lead, to obtain the quantity of oxide of lead con- 

 tained in the 12-27 of arscnite of lead; that is to say, 6-47 of 

 oxide of lead were combined with 5-82 of arsenious acid. Hence 

 the salt is composed of 



Arsenious acid 47-356 100-00 



Oxide of lead 52-644 111-17 



100-000 



Now these 111-17 parts of oxide of lead contain 7'95 of oxygen, 

 which multiplied by 4 = 31-8 ; so that the arsenious acid contains 

 four times as much oxygen as the base which it saturates. 



In my former experiments with arsenite of lead, I found 100 of 

 arsenious acid combined with 1 18-9 of oxide of lead, which 

 induced me to believe that the arsenious acid neutralized a quantity 

 of base containing ^ of the oxygen of that acid. We see that with 

 respect to tlie composition of this arsenite my former experiments 

 agree sufficiently with the present ones, though neither of them 

 probably are quite exact : but as to the consequence to be drawn 

 from them resijectiiig the composition of arsenious acid, it is 

 clearly different from what I formerly drev/. 



To see whether arsenious acid be capable of forming subsalts, I 

 prepared a subacetate of lead as free as possible from neutral 

 acetate and from the subacetate at a maximum. I precipitated a 

 solution of this subacetate by means of arsenite of ammonia, 

 taking care not to precipitate the whole of the lead. This precipi- 

 tate being well washed and fused, 1 dissolved 10 parts of it in nitiic 

 acid, and decomposed it by sulphuric acid with the precautions 

 mentioned above. I obtained 9-32 parts of sulphate of lead. Hence 

 this subarsenite is composed of 



Arsenious acid .^ 31-3 100-0 



pxide of lead 6S-7 2iy-i» 



iOO-0 



