66 REPORT—1858. 
different hours of the day, and under altered conditions of rest, exercise, or fatigue. 
The small amount contained in the atmosphere inspired is quite inadequate to ac- 
count for that excreted, and we must consequently regard it as produced within the 
body. The albumen and fibrine of the blood suggest themselves as capable of sup- 
plying the nitrogen and hydrogen requisite. If we may assume the blood to be the 
source of animal ammonia, let us look at the exquisite balance of chemical forces in 
its connexion with that fluid. Blood is feebly alkaline from fixed alkali or alkaline 
salt; not sufficiently so to hold fibrine in solution by this agency, but to a degree which 
ensures the volatile alkali being left free for this purpose, when formed in the closed 
chambers of the circulation. This view harmonizes with the fact, that the formation 
of ammonia is a continuous process; the portion which maintains fluidity at a given 
moment does not remain to exercise this office for hours or days; but carrying the 
fibrine to every part of the body to supply its waste, it is itself eliminated by the 
excretory surfaces. 
On the Practical Application of Aluminium. By R. Reynoxps, F.C.S, 
The author presented for examination by the Section, a spoon made of this metal 
by Messrs. Coulson and Co., Sheffield. In this form, its lightness, as compared with 
the metals ordinarily used for such purposes, was very striking. A perfect polish 
had been attained, but its zinc-like tinge of colour made it differ from silver in 
appearance. The handles of a knife and fork by the same manufacturers were also 
exhibited. They closely resembled gold in colour, and were composed of an alloy of 
copper with 5 per cent. of aluminium. — By varying the per-centage of the last-named 
metal from 5 to 10, any shade of gold colour is attainable. 
On the Choice of Subject in Photography, and the Adaptation of different 
Processes. By W. L. Smitu. 
On a new Method of Determining the Quantity of Carbonic Acid contained 
in the Air. By Dr. E. Smtru. 
On some Double Salts formed with Bichromate of Potash. 
By W. K. Sutxivan. ; 
In the description given in Gmelin’s ‘ Handbuch,’ of Fritzsche’s process of pre- 
paring chromic acid, it is recommended carefully to add a warm solution of bichromate 
of potash to an excess of oil of vitriol, as any, excess of the salt would crystallize out 
without being decomposed, and thus contaminate the chromic acid. It appeared to 
me improbable that bichromate of potash would separate under such circumstances ; 
and having had occasion recently to notice the salt which separates, I found that it 
did not present the characters of bichromate, and that it contained sulphuric acid. 
If a nearly boiling concentrated solution of bichromate of potash be treated with 
sufficient oil of vitriol to convert the whole of the potash into bisulphate, but not to 
precipitate the chromic acid, and be then set aside, an abundant crystallization of 
anhydrous bisulphate of potash will be formed. The crystals thus formed are often of 
considerable size, and beautifully exhibit the peculiar reaction of the anhydrous bi- 
sulphate with water, namely, of swelling up and becoming opake. The crystals are 
always coloured yellow by the adhering solution, but sometimes they appear to 
contain some chromate in combination ; for even after having been repeatedly dried 
between folds of filtering paper, they yielded a mixture of bisulphate of potash in 
acicular needles and orange-red rhombic needles, when dissolved in water and 
recrystallized. 
When somewhat less oil of vitriol was employed than in the last case, a beautiful 
salt composed of orange-red rhombic plates separated, which were readily decomposed 
by water, exhibiting the same phenomenon as the anhydrous bisulphate, When a 
quantity of the transparent crystals were placed upon a filter and washed with water, 
they gradually became opake, swelled up and changed to a pale orange yellow mass. 
When the washing was not carried too far, and the filter was placed upon a plate of 
dry plaster of Paris, so as to absorb the moisture, the substance still exhibited the 
