On definite Proportions. 377 
418°977 parts of the protoxide contain 8*5068 of oxygen, 
the arsenious acid should, upon that supposition, contain in 
100 only 17°0136 of oxygen to 8379864 of metal ; and this 
is not reconcileable with any of the analyses of ‘Bucholz, 
Rose, Thenard, and Proust. If however the arsenious acid 
contains three times as much oxygen as the protoxide sa- 
turated by ii, its composition will stand thus: 
Arsenic...) 74°48 100°000 
Oxygen... 25°52 34263 
And this determination agrees very nearly with that of 
the chemists who have been mentioned. 
Arseniate of the protoxide of lead. 1 dissolved 10 gr. of 
very pure arseniate of the protoxide of lead, which had | been 
ignited, in diluted initrie acid, and precipitated with sul- 
phate of ammonia. The clear liquid was evaporated to 
dryness, and the dry mass, still acid, was dissolved in water. 
It left a pretty considerable quantity of sulpbate of the prot- 
oxide of lead, and still more was thrown d: wn upon satu= 
rating the Auid with caustic ammonia. The precipitate, 
when collected, well washed, and ignited, weighed 9-559 or. 
As this result did not agree with the determinations of 
Klaproth and Rose, I repeated the experiment with 6 gr. of 
the arseniate: and the sulphate, which 1 obtained from it, 
weighed 5°731 gr. and this agrees very nearly with the fit. 
mer experiment. As Klaproth and Rese did not remark 
the solubility of the sulphate in the mixture of the two 
acids, this circumstance was probably the reason that they 
found the quantity of Jead smaller than I did. For when I 
decomposed 10 gr. of the arseniate, by means of sulphate 
of soda, without saturating the superfluous acid, I obtained 
only *0:042” [9:042?] gr. of ignited sulphate, which 
agrees exactly with the result obtained by those chemists. - 
fence the arseniate of the protoxide of lead consists of 
Arsenic acid .. .. 29°6317 100°0 
Protoxide of lead... 70°3683 237°5 
T thought it probable that a superarseniate of lead might 
also exist, containing only half as much of the base as the 
neutral combination, and consisting of the acid united with 
the base in the same proportion as in the arsenite. I there- 
fore dissolved some of the arseniate in nitric acid, slow] 
evaporated the solution until it crystallized, and collected 
the salt: it was however not such a compound as I ex- 
pected, but a double combination of arseniate and nitrate 
of the protoxide. It was decomposed by water; the nitrate 
was dissolved, the crystals Jost their transparency, and the 
arseniate 
