576 
POPULAR SCIENCE REVIEW. 
immerse the bottle in hot water and agitate occasionally until completely 
dissolved. When cool, the solution is poured into a flat dish, and sheets 
of paper immersed therein, and after a few minutes removed, drained, and 
dried ; they are then salted by floating upon a solution of chloride of 
sodium (ten grains to the ounce of water), to which a small quantity of 
Iceland moss has been added. In order to Sensitize this paper, it is treated 
in the usual manner with a 60-grain solution of nitrate of silver. 
The recovery of gold and silver from the waste solutions and products of 
a photographic laboratory has been proved by Mr. England to furnish very 
lucrative results ; many pounds’ weight of an alloy of these precious 
metals having been recovered from the various residues obtained in the 
printing operations carried on at his establishment. The paper read by 
that gentleman at a meeting of the London Photographic Society, on the 
5th May, details the steps to be taken in order to effect this saving. 
The partial eclipse of the sun visible on the 17th May last, and the total 
eclipse of the moon on the night of the 1st June, were events which do 
not appear to have claimed from photographers the amount of attention 
which such interesting occurrences undoubtedly deserve. Among the 
records of the solar eclipse which have come under our notice are those of 
Mr. W. Deane, taken at Richmond, and a series of five larger representa- 
tions which were photographed at Woolwich by Mr. Spiller. The appear- 
ance at the moment of maximum obscuration is well shown in the latter 
series, whilst Mr. Deane’s picture shows likewise a peculiar kind of solar 
radiation, which assumes somewhat the figure of a cross. 
The remarkable photographic observations made by Mr. Glaisher during 
his last balloon ascent excited a great deal of attention ; the principal fact 
may thus be stated : At an altitude of three miles, with the thermometer 
registering 21 degrees Fahrenheit, and in the clear atmosphere above the 
clouds, it was found that sheets of sensitized photographic paper were less 
affected in colour during thirty minutes’ exposure than were similar papers 
held in the sunlight at about the same time, but for one minute only, 
within the grounds of the Royal Observatory, Greenwich. Many opinions 
have been offered by way of accounting for these curious results ; and it 
seems generally admitted that the dry condition of the air would naturally 
induce a state of inactivity in consequence of the removal from the paper 
of water, which is so necessary in all these cases for the purpose of aiding 
chemical decomposition, upon which the darkening in colour depends. 
In apparent contradiction to these results are the former observations 
of Professor C. Piazzi Smyth, who states that during his ascent of the 
mountain in Teneriffe he remarked a gradual increase of chemical activity 
just in proportion as he gained in altitude ; and that in using the camera 
near the summit he found that the exposure might be very much curtailed. 
To settle this apparent discrepancy Mr. Negretti recently made an ascent 
from Sydenham in Mr. Coxwell’s mammoth balloon, taking with him a 
camera and all the materials requisite for carrying on the practice of the 
collodion process ; the car itself being fitted up as an operating-room. 
He likewise found that the time of exposure at great altitudes might be 
very much shortened. It thus appears that in the camera , as in all cases 
where it is impossible for the water to evaporate from the film or other 
