70 Photographie Notes. 
360.—Urinary Deposits.—What is the best and simplest way 
of staining and mounting urinary deposits ? PHYSICIAN. 
361.—Plants.—How is it accounted for that plants under the 
influence of sunlight by day emit oxygen, whilst at night they 
emit carbon dioxide gas ? W. 
362.—Double Rose.—Assuming that the double rose is an 
artificial product, I should much like to know when it was first 
produced. Is it known whether the roses which the Roman 
poets (Horace, for instance) speak of were the artificial double or 
the natural single rose, like the rose of our hedges ? Rw Sark: 
363.—Explosion of Potassium.—The other day, in attempting 
to take a piece of potassium from a bottle with the point of a dry 
penknife, the whole thing exploded, the mineral naphtha, as well 
as the potassium, taking fire and giving me a severe burn. Some 
months since, a morsel of metal from the same bottle, when 
touched, flew across the room with explosive violence. Can any- 
one account for this, as there was no moisture present in either 
case P . ACE 
364.—Removing Grease.—Will any reader of the Euguirer 
kindly inform me what is the best way of removing greasiness 
from entomological specimens? I have seen French chalk 
recommended, but have been afraid to risk utterly ruining speci- 
mens which cannot be replaced, by trying it without further 
information on the subject. Is it sprinkled over the wings and 
bodies, and if so how can it be got off again without removing a 
large proportion of the scales? Benzine is also recommended, 
but although a small quantity of it does not do the specimens any 
harm, yet if they are soaked in it all the scales will cling to- 
gether. I have tried it with partial success, but the results have 
not been so satisfactory as I could wish, and therefore I shall be 
glad of any information as to the use of French chalk. 
G.2EE OB. 
Photographic Notes. 
Magnesium Flash-Light.—I would most strongly warn all 
amateurs against the compounds of magnesium’ and chlorate of 
potash. Unless very carefully used, they may have a most 
unpleasant “blow-up” when they least expect it. Gun-cotton 
works very well, but cannot always be procured. ‘‘Schultze” or 
“ Coohal” powder will do just as well, and can be had from any 
gun-maker. It will easily powder between the fingers, and can 
then be mixed with the magnesium powder. A very handy lamp 
for burning it in is made out of a 5-H. “E. C.” or “Schultze” 
