SCIENTIFIC SUMMARY. 
533 
The excellent photographs of MM. Ghemar Freres, and of Oehme and 
Jamrath, of Berlin, and the panoramic views of Florence, are well worthy 
of close inspection ; and there is much to admire also in the way of photo- 
graphic apparatus and chemicals of foreign manufacture, especially the 
cameras of M. Emile Busch, of Potsdam, and the monster sample of finely 
crystallized pyrogallic acid sent by M. Schering, of Berlin. 
The expenditure of silver in the photographic processes has been lately 
made the subject of investigation by Mr. W. T. Mabley, who has commu- 
nicated the results of his experiments to the Manchester Photographic 
Society. It appears that in the preparation of a full-sized sheet of sensi- 
tized albumen paper no less than sixty grains of nitrate of silver are with- 
drawn from the solution when of the strength of seventy grains to the 
ounce of water; but by careful management a very large proportion of this 
amount may be recovered in the form of insoluble salts of silver, such 
as the chloride and sulphide, which may again be reduced to metal. 
Mr. Mabley states, as the result of his operations upon fifteen sheets of 
albumenized paper, that he succeeded in collecting 350 grains of chloride 
of silver from the nitrate washings of the prints, and 180 grains of metallic 
silver reduced from the hyposulphite fixing-bath. If from these numbers 
the average saving be calculated, it will be found that more Than three- 
fourths of the silver originally employed in the preparation of the paper 
should be recovered in the form of residues. In the course of his state- 
ment, Mr. Mabley describes a novel method of detecting and precipitating 
small quantities of silver from the hyposulphite solutions. It consists in 
adding caustic soda until alkaline, and boiling with a little grape-sugar, 
when the least trace of silver in the liquid will manifest its presence by 
the formation of a metallic deposit of reduced silver. 
A series of comparative experiments are recorded in the “American 
Journal of Photography,” which have for their object the determination 
of the relative degrees of sensitiveness possessed by albumenized paper which 
has been treated with the plain nitrate and with the ammonio-nitrate of 
silver. Paper prepared with the latter agent is shown to be more readily 
affected by light, and easily toned ; but there are, at the same time, some dis- 
advantages attending the employment of ammonio-nitrate of silver with 
albumen, in consequence of which it is recommended to sensitize the paper 
by floating upon a neutral solution of nitrate of silver, and afterwards to 
expose the dry sheets to the fumes of concentrated ammonia in a large glass 
bottle or cylindrical jar. 
The American operators have likewise been experimenting upon new 
materials for the construction of the dipping-bath used in the collodion 
process. Glass, porcelain, gutta-percha, and, more recently, ebonite, have 
been successfully employed ; but the last idea is to try the application of 
wood : the result has proved a failure on account of the decomposing action 
exerted by the salts in the wood upon the solution of nitrate of silver. 
It is the common misfortune of photographers to experience a difficulty 
in preserving the nitrate bath in the most sensitive condition, without 
exhibiting a tendency to produce “ fogging ” on the development of the 
collodion picture ; and when this condition is practically realized, the most 
trivial disturbing cause will often overturn that nice degree of neutrality 
NO. IV. 2 0 
