SCIENTIFIC SUMMARY. 
131 
renewed exposure. The test solution may be prepared by dissolving about 
10 grammes of molybdate of ammonia in an excess of diluted sulphuric 
acid ; metallic zinc is then introduced until the liquid has become dark- 
blue, and then a solution of permanganate of potassa is carefully added 
until the colour is again bleached. 
The state of dilution is not specified by the author, but in applying this 
principle to the determination of the chemical and solar intensity, it is 
proposed to employ measured portions (20 cubic centimetres) of the same 
standard solution for a like period each day — say from eleven until twelve 
o’clock. The amount, or rather degree, of discolouration is then estimated 
by gradually adding a solution of bichromate or permanganate of potassa 
of known strength, until the last drop restores the liquid to its primitive 
colourless state. 
An ingenious method of printing blue photographs, founded upon the 
old Prussian-blue process of Herschel, has been devised by Mr. Carey Lea. 
He floats the paper for a very short time on a solution of the double 
peroxalate of iron and ammonia. It is then thoroughly dried in the dark, 
and exposed under a negative for a space of time varying from two or 
three minutes in the sun to twenty or thirty in the shade. On re-entering 
the dark room no impression is visible on the paper, but the print is rapidly 
developed when immersed in a mixture of four parts saturated solution of 
oxalic acid, one part ferricyanide of potassium, and twenty-five parts of 
water. After the image has acquired full intensity it only requires wash- 
ing in water. The double oxalate is prepared by dissolving hydrated 
peroxide of iron in binoxalate of ammonia. The chief improvement 
consists in adding oxalic acid to the developing bath. This keeps the 
whole parts perfectly clean, — a difficult point to manage by the old 
processes. 
A very pretty application of photography to the ornamenting of glass 
and porcelain surfaces has just now been announced as the invention of 
M. Beyrich, the well-known manufacturer of enamelled photographic 
papers, of Berlin. The process cannot yet be said to have been fully 
perfected, but the following details will convey a general idea of the mode 
of proceeding : — Positive impressions are first obtained by printing from a 
glass negative upon a particular description of photographic paper, the 
copies being made rather darker than usual, and fully toned ; they 
are fixed in hyposulphite of soda, and subsequently well washed in water. 
In this last operation it will, however, be noticed that the sensitive film, or 
rather the actual picture, gradually separates from the substratum of 
ordinary paper, and ultimately becomes disengaged, floating in the water 
as a perfect, though extremely delicate, photographic film, which can, by 
careful management, be lifted upon a flat plate of opal glass, or received 
even upon rounded surfaces, as those of a porcelain vase. Being adjusted 
at once into the desired position, the photograph is then allowed to dry, 
and requires merely the employment of a thin coating of some transparent 
varnish to secure its perfect adhesion to the surface either of glass or 
porcelain, and, at the same time, will be sufficiently protected against 
injury to permit of the method being applied to a great variety of orna- 
mental purposes. The special paper is supplied by its inventor, and its 
K 2 
