MISCELLANY. 
351 
On the Blackening of Nitrate of Silver by Light, by M. Scanlan.— 
Nitrate of silver was recommended many years ago, as well as I remem- 
ber, by Dr. John Davy, as a test of the presence of organic matter in 
distilled waters. He showed, that if nitrate of silver in solution be added 
to perfectly pure water, it is not altered by exposure to direct sunshine; 
but if the water contain a trace of organic matter, it will become black- 
ened. It would seem to follow, as a matter of course, from this, that 
solid nitrate of silver is not blackened by exposure to light, (although 
the contrary is stated in almost every work on chemistry,) unless it be in 
contact with organic matter; and this we find to be the case by experi- 
ment. Mr. Fergusson, some years ago, when he had the management of 
the chemical laboratory belonging to the Dublin Apothecaries' Company, 
first showed me, that perfectly pure nitrate of silver is not blackened by 
long exposure to direct sunlight, but I believe he never gave further 
publicity to this fact, than mentioning it to his chemical friends in Dublin 
at the time. In consequence of some observations upon the blackening 
of this salt, made by Dr. Aldridge, of Dublin, in his review of Mr. 
Phillips's translation of the London Pharmacopoeia, I was led to make 
the following experiment upon the subject : — I took two cylinders of per- 
fectly pure fused nitrate of silver, immediately as they were cast from the 
mould, and wrapped one of them in paper, in the usual way that it is found 
in the shops; the other cylinder was transferred to a glass tube, and 
sealed up hermetically, by means of the blow-pipe, without being suf- 
fered to come in contract with organic bodies : it was pushed from the 
mould into the tube by means of a glass rod. After a lapse of three 
days, the paper was removed from the first, and it was then sealed up in 
a tube, in a similar manner to the other. The two tubes were now ex- 
posed to the direct rays of the sun, and in half an hour the nitrate of 
silver that had laid in contact with paper was blackened, while that in 
the other tube was not altered by six weeks' constant exposure. The 
whole amount of blackening of the cylinder that had been papered was 
produced in the half hour. Nitrate of silver, free from organized matter, 
is sometimes blackened. I find, by exposure to the air; but this may be 
owing to the presence, perhaps, of sulphuretted hydrogen, accidentally 
present. Atmospheric air, too, is, I believe, seldom free from organic 
matter, at least in London, as may be seen readily by looking through a 
sunbeam. — lb. 
On the Decomposition which is produced by the Action of Emulsin on 
fimygdalin, by Dr. R. D. Thomson and Mr. T. Richardson. — Some 
years ago, Robiquet and Boutron-Charlard showed, that volatile oil of 
bitter almonds and prnssic acid, which are obtained by the distillation of 
bitter almonds, do not exist naturally in the almonds, but result from the 
process. They further ascertained, that when milk of bitter almonds. 
