1874.] Phystes. 273 
PHYSICS. 
Microscopy.— The Quekett Microscopical Club has recently been presented 
with a series of insect preparations in balsam, from Ceylon. They are remark- 
able, inasmuch as the usual eviscerating and laying-out processes have not 
been adopted, but the insects mounted as much as possible in their natural 
position, and with the minimum amount of compression: the preparations are 
in many cases very thick, but this is no disadvantage, but rather the contrary, 
for observations with low powers and the binocular microscope. The insects 
were merely dried between the leaves of a book, and then mounted in balsam, 
sometimes after a soaking in turpentine; liquor potasse has in no instance 
been employed. The hardening of the balsam has been effected entirely by 
exposure to the sun; the collection is totally free from milkiness from damp, 
and the penetration of the balsam is perfect. This mode of preparation is, of 
course, only available in tropical climates. Such preparations would probably 
be best made here by drying the insects by immersion in absolute alcohol, then 
soaking in oil of cloves, and, when the preparation has cleared, mounting in 
balsam. This process is much used on the Continent for anatomical subjects, 
frequently stained and injected, and is but little known in this country: it will 
be found invaluable where other modes of drying cannot be made available. 
In illustrating a paper on the ‘ Life-History of Monads,” read before the 
Royal Microscopical Society, the Rev. W. H. Dallinger, F.R.M.S., executed 
the drawings in a manner which rendered them available for lecture illustration 
with the magic-lantern. The material chosen is finely-ground glass, upon 
which the drawing is made as readily as upon paper: the camera-lucida, or 
other instrument, is available for obtaining the sketch from the microscope. 
The pencils used should be harder than those employed in drawing upon 
paper; the engraver’s 6H will prove useful, HB being strong enough for the 
deepest shadows. When the drawing is finished, it is to be rendered trans- 
parent by the application of Canada balsam, thinned with benzol to the con- 
sistence of cream: this is poured on the plate, and evenly distributed, some- 
what in the manner of collodion in photography. When hard, the varnished 
surface is protected from injury by a glass fastened on it by strips of paper 
at the edges, with small pieces of card at the corners to prevent contac. 
Water-colour is available upon the ground-glass surface. The process will be 
found in every way easier than the usual mode of producing magic-lantern 
slides, and equally effective. 
The “ Sand-blast”’ process has been*successfully employed by Mr. H. F. 
Hailes, of the Quekett Club, for excavating hollows in glass slides to be used 
as cells. For dry mounting they answer admirably, and the roughness of the 
bottom is no hindrance to mounting objects in balsam, as the lower surface of 
the cell is rendered perfectly transparent by contact with the mounting 
material. 
Messrs. Underhill and Allen communicate to the March number of ‘‘ Science 
Gossip” the following formula for glycerin jelly :—‘ Soak } oz. best amber 
gelatin (as sold by the chemist or grocer) in r oz. distilled water; when it has 
absorbed all the water, put it in a Florence flask with 50 grains of powdered 
chloride of barium; warm it in a water-bath, and agitate till the barium salt 
is dissolved. Allow it to cool below 35° C., and while still fluid add 1 oz. 
of Price’s glycerin and a teaspoonful of white of egg; shake until well mixed, 
replace in the water-bath, and boil at full speed until the albumen completely 
separates from the jelly in the form of a single lump. Now filter through 
well-washed fine flannel, and it should be as clear as crystal; but if through 
Mismanagement it be a little cloudy, filter it again, this second time using 
filtering-paper, and placing the funnel with the jelly, &c., in a ‘cool’ oven. 
During the coagulation of the albumen, the jelly must on no account be 
stirred. It is well to beat up the white of egg before use, lest it should be 
stringy. The jelly made after this recipe is of the proper consistency for 
entomological objects, but for delicate vegetable structures it should be softened 
by adding to it a third of its volume of a mixture of equal parts of glycerin 
