BUNSEN ON THE CACODYL SERIES. 285 
published, I should have considered a detailed exposition of 
them here as unnecessary, had not Dumas more lately asserted 
the truth of his former experiments on the same subject, which 
do not correspond with my results. 
Although this celebrated chemist does not appear to have 
prosecuted his experiments so far as the nature of the difficul- 
ties connected with them seemed to require, deterred perhaps 
by the offensive characters of the substance, yet I cannot hesi- 
tate to oppose the following results to an authority such as his, 
even where he has himself regarded his own results as decisive. 
He determined the arsenic partly by oxidation with aqua 
regia in a retort which was connected with a receiver, collecting 
the liquid condensed and weighing the arsenic acid after it had 
been thoroughly dried; partly also by conducting oxygen gas 
through the combustion tube till the arsenic was perfectly 
oxidized, and then determining the weight of the arsenious acid 
formed by the loss of weight in the combustion tube. In the 
first instance he obtained 69°3 per cent., and in the second 68°93 
and 69:0 per cent. I have also, in my former paper on this sub- 
ject, detailed an experiment in which I obtained a result similar 
to the first of Dumas; but with this difference, that the oxida- 
_ tion of the arsenic was conducted in a glass tube hermetically 
sealed, and the arsenic estimated not as arsenic acid, but as 
arseniate of iron. Any loss of arsenic in my experiment was 
‘therefore impossible. Nevertheless I only obtained, under the 
most favourable circumstances, 64°2 per cent., and consequently 
less than I ought to have had according to theory. I formerly 
attributed this loss to the imperfect oxidation of the arsenic, 
which may be easily shown by heating the solution, which has 
no smell, with chloride of tin or sulphuretted hydrogen. In the 
first case the frightfully penetrating and stupifying smell of 
chloride of cacodyl appears, and in the latter the no less cha- 
racteristic odour of sulphuret of cacodyl. The solution must 
therefore have contained alcargen (cacodylic acid), which is not 
decomposed even by evaporation to dryness, and being reduced 
by the above deoxidizing agent is converted into the correspond- 
ing sulphur and chlorine compounds. It is therefore probable 
that the substance analysed by Dumas was not pure, or that the 
arsenic acid from which the weight of the arsenic was deduced 
had retained some water. Neither could the other method by 
weighing the combustion tube atiord an accurate result, which 
