90 
THE YOUNG SCIENTIST. 
popular and favorite meeting places of valu- 
able specimens. 
Trap for Moths. — An old tea chest or 
grocer's box forms the basis of a good trap. 
By reference to the figure the construction 
D 
Fig. 2. 
is easily understood, and it may be made 
by any boy. The box, A A, has a circular 
hole cut in one side, and a coarse canvas or 
wire gauze funnel fastened in at B. The 
bottom may be covered with the sugar and 
treacle described above, and this covered 
with gauze or canvas, C. A small door at 
D, with leather hinges, and fastened with a 
button, will be convenient for taking out 
specimens. This trap, when set in a field at 
night, will often contain next morning a 
large number of beauties. 
Sweeping. — For securing a variety of 
small moths, flies, beetles, etc. , the process 
called sweeping is very successful. The net 
is here used by walking through a field of 
grass or stubble, and constantly sweeping it 
back and forth in a half circle ahead of the 
collector, the net just clearing the ground. 
An infiinite variety of insects will be ob- 
tained by this method, out of which select 
those cared for, and confine in small pill 
boxes or envelope corners. 
Setting Small Insects. — Insects that are 
too small or too delicate to be pinned, are 
easily mounted on cardboard or very stiff" 
white paper. A sheet of cardboard may be 
covered with specimens, and when full cut 
into squares, each square containing an 
insect. Thick gum arabic water, with a 
very little corrosive sublimate (poison) 
added, makes a good gum for fastening the 
specimens to the cardboard. A spot about 
the size of the insect should be gummed, 
the specimen placed on this, the legs ad- 
justed and then allowed to dry. 
Bemember to keep the record of all col- 
lections, with date, locality, number, etc. 
Larva. — The collector will often find 
worms, grubs and caterpillars; these are the 
larvse of future moths and butterflies, and 
should be saved, especially those that are 
found feeding. A few of the leaves they 
are feeding upon should be taken, with 
which to feed them until they spin. The 
large green worms found on fennel, tobacco, 
parsley, carrot tops, elm and mulberry 
trees, are valuable, and much amusement 
and instruction will be derived by watching 
them during their transformations. They 
may be put in paper boxes, with their food 
and most of them will spin, though some 
species will bury themselves in the ground 
and enter the pupa state without forming 
cocoon. For this reason it is advisable to 
put a little earth in each of the boxes, and 
when the larva is inclined to dig, transfer 
it to a jar or tin fruit can nearly filled with 
earth. All larvae should be kept in a warm 
place, which will hasten their transforma 
tions. 
To he continued. 
Simple Lessons in the Art of Photo 
graphy. 
COLLODION. 
COLLODION is a solution of gun-cotton 
in sulphuric ether and alcohol. Cot 
ton consists chemically of carbon, hydro 
gen and oxygen; gun-cotton contains an 
additional element, namely, nitrogen, which 
renders it explosive. Photographic gun 
cotton, that is, the gun-cotton used in pho 
tography, is not so explosive as gun-cotton 
used for military purposes, but it is per 
fectly soluble in a mixture of ether and 
alcohol. The technical name for gun-cotton 
in photography is Pyroxyline. 
Cotton or filtering paper is transformed 
into pyroxyline by immersion into a mixture 
of nitric and sulphuric acid. Only the 
finest cotton or the best Swedish filtering 
