BUNSEN ON THE CACODYL SERIES. 289 
possible care, and employed the very best instruments. We 
must also recollect, that a difference even quite within the limits 
of observation and experiment in vapours of great density, 
exercises a serious influence on the ultimate result; that these 
errors of observation increase with the boiling point of the fluid ; 
and lastly, that the small quantity of protoxide with which the 
mercury is mechanically mixed, may occasion a considerable 
oxidation of the alcarsin. 
The experiments do not therefore leave any doubt that the 
composition of the alcarsin is represented by the empirical for- 
mula C, H, As, O; and the order in which these elements 
are grouped among themselves, is no less clearly shown in the 
transformations which this substance undergoes. When we 
observe that it is the oxygen which is increased or diminished, 
displaced or substituted ; when we observe, further, that these 
changes do not take place with the carbon, arsenic, or hydrogen, 
which remain united together in the same relative proportion, 
in the long series of these compounds, we are compelled to re- 
gard this unchanging atomic group as a collective member, a 
unity, and as such only to play a part in the decompositions of 
this class of bodies. This member, which we call cacodyl, and 
denote by the expression C, H, As, = Kd, passes from the region 
of hypothesis to that of reality, when we find in it those laws 
and characters which are now regarded in our science as suffi- 
cient to justify us in forming some conception of the constitution 
of inorganic bodies. How far this is applicable to the class 
of bodies before us, will be seen from the following researches. 
If we apply this view to explain the constitution of alcarsin, 
we must regard it as the lowest degree of oxidation of cacodyl, 
and represent it by the rational formula C,H, As, + O = Kd O. 
The characters which we observe perfectly accord with this view. 
It is a saline base, and approaches those inorganic oxides which, 
although possessing the characters of weak acids, must be re- 
garded as bases. It does not react either alkaline or acid, but 
unites with acids and forms peculiar substances soluble in water. 
Phosphoric acid dissolves a considerable quantity, and forms 
an offensive viscous fluid, which can neither be crystallized nor 
rendered neutral. When it is heated, pure water at first passes 
off, and then mixed with alcarsin, which retains all its characters 
unchanged, and the phosphoric acid remains behind quite pure 
in the retort. 
