SCIENTIFIC SUMMARY. 
209 
nitric acid in the previous cleaning than that which may he necessary to 
clean the diatoms themselves ; and the use of sulphuric acid and chlorate of 
potash is not required, as the bleaching of the unsightly foreign material 
would be useless. A large drop of the prepared material must bespread 
near the edge of a glass slide ; the appearance of this under a simple micro- 
scope with a glass of one-inch focus will be that of much dirty material 
containing a few clean diatoms ; the best of these latter may be pushed out 
of the water by means of a needle, and nicely arranged near the centre of 
the slide. The slide may now be raised, and the water may be carefully 
wiped off ; the turning of the slide on its edge, or the wiping away of the 
water, will not disturb the diatoms selected and placed, as they remain 
attached to the glass sufficiently firmly to admit of the movements required. 
In this way the choice diatoms may be selected out of many drops, and be 
perfectly free from an unsightly speck of the half-cleaned foreign material. 
PHOTOGRAPHY. 
New Fhotocrayon Process. — Mr. Sarony, photographer to the Queen, 
Scarborough, has recently introduced what he designates photocrayon 
portraits. They have furnished material for discussions at the London 
photographic societies and in the journals devoted to the art. The position of 
Mr. Sarony as the principal of one of the largest photographic establishments 
in the kingdom, and as an artist of skill and taste, has secured for his new 
crayon photographs the favourable attention of his brethren. The portrait is 
executed on a glass plate fourteen inches in size, and is an enlarged vignette 
from an ordinary carte negative. The method by which they are produced 
is simple in the extreme. The negative is inserted, as a slide, into a 
magic lantern, and the enlarged image is thrown upon a sheet of glass 
previously made sensitive by being collodionised and excited in a 40-grain 
nitrate of silver bath. When magnesium ribbon is employed as the source 
of illumination, an exposiu’e of half-a-minute suffices to impress an image, 
which, after development with a solution of pyrogallic acid one grain, and 
citric acid one and a-half grain in each ounce of water, is fixed with 
hyposulphite of soda, washed, and varnished. In this state it is a trans- 
parence, the whites of the picture being represented by clear glass, and the 
shadows by a dark deposit of silver more or less intense. It is now backed 
by a piece of drawing paper of any desired tint, on which hatchings by a 
crayon have been made so as to surround and, where necessary, merge into 
the figure. The effect of the whole is that of a photograph on drawing 
paper, skilfully finished in crayon or chalk, the hatchings by which the 
vignetted subject merges into the ground of the picture conferring what is 
termed an artistic’’ appearance, and conveying the belief that the picture 
has been elaborately worked upon by the artist j whereas the hatchings on 
the backing papers are printed by lithography. It is a mechanical method 
of producing art imitations of wrought-up photographic enlargements 
which will probably be much adopted. The rough texture of the backing 
