, 
378 On definite Proportions. 
arseniate fell down as a white powder: so that it seems 
impossible to obtain a superarseniate of lead. 
Arsenic acid. When | attempted to deduce the compo- 
sition of the arsenic acid from these data, I thought at first 
that it could not contain less than three times as much 
oxygen as the protoxide of lead neutralized by it; and in 
this case more than half of it must have been oxygen. It 
could therefore only contain twice as much oxygen as the 
base; for 237°52 parts of the protoxide contain 16°981 of 
oxygen, and 16°981 X 2=33°962. According to this cal- 
culation, therefore, the arsenic acid consists of 
Arsenic .... 66°038 100-000 
Oxygen.... 33°962 51°428 
But 100 parts of metallic arsenic take up 34°263 of oxy- 
gen in order to form arsenious acid, and 34263 x 1i= 
51°3945, which differs from the number already found, by 
*0335 only. Consequently the arsenic acid follows the 
‘same steps, in its different states, as the sulphuric and the 
oxymuriatic acids, the oxide of iron, and the yellow oxide 
of lead. 
What differences however are still observable in the 
midst of these analogies! The sulphites take up oxygen, 
without altering their internal composition, and become 
sulphates. The phosphites part with a portion of their 
phosphorus, which becomes phosphoric acid, and the hy- 
peroxymuriates become muriates while they emit a part of 
their oxygen. The arsenites, on the other hand, are only 
altered in the fire by the addition of oxygen, since they 
contain more arsenic and more oxygen than the arseniates : 
but if a portion of the arsenious acid can be more highly 
oxygenized, it expels another portion, equal to itself in 
weight, from the mixture. These are appearances which 
might have been deduced from our general views, without 
the necessity of observing them. It is remarkable that all 
these double acids, derived from the same radical, have dif- 
ferent laws with respect to their powers of saturating a given 
base. The sulphuric acid contains half as much more oxygen 
as the sulphurous which is capable of saturating the same 
base; the phosphorous and the phosphoric contain equal 
quantities ; the arsenious contains half as much more as the 
arsenic ; while the hyperoxymuriatic, as we shall hereafter 
see, must contain three times as much oxygen, for a given 
quantity of a base, as the simple muriatic. 
Metallic arseniets or arseniurets. In the sulphites, as 
‘well as in the sulphates, the metal of the base is combined 
with 
eee 
