336 Messrs. J. Spill er and W. Crookes's Researches on the 



In regard to sensitiveness, they will, if used immediately, be found 

 veiy little inferior to plates prepared in the ordinary way; we 

 have, however, detected evidence of slight deterioration in pro- 

 portion to the length of time the exposure has been deferred. 

 In cases where it is necessary to keep the plates ready excited 

 through a protracted interval, we have devised a convenient 

 plate-box to store them in, which may easily be made by replacing 

 the wooden grooves in an ordinary plate-box by two corrugated 

 sheets of gutta percha, and laying a square of thin caoutchouc 

 at the bottom for the glasses to rest upon. Such a box will 

 always require an outer covering to protect its contents from 

 every gleam of light, the necessity for which precaution, as also 

 that of excluding injurious gases, such as ammonia and sul- 

 phuretted hydrogen, will be sufficiently obvious without further 

 comment. 



Before proceeding to develope the latent image on the glycerine 

 plate, it is only necessary to immerse it for two or three minutes 

 in the 30-grain niti-ate of silver bath, when the solution of pyro- 

 gallic acid or protosalt of iron may be applied as usual ; the 

 remaining part of the process, fixing, &c. being conducted in the 

 oixlinary manner. 



The negative pictures resulting from this mode of treatment 

 have not, in our hands, been found wanting either in intensity 

 or in gradation of tone ; they are in fact fully equal to the results 

 of the collodion process as usually practised. 



If considered desirable, a bath of the mixture of glycerine 

 and nitrate of silver may be employed, instead of the mode of 

 application recommended above ; in that case it will be neces- 

 sary to protect the fluid from the light, so as to avoid the depo- 

 sition of metallic silver ; and on that account, to make use of a 

 covered gutta-percha in preference to a (jlass bath for containing 

 the solution. The remarkable purity of Price's glycerine, its 

 absolute freedom from chlorides (and sulphates), renders the 

 plan of mixing only as required for use far more practicable than 

 would otherwise have been the case, had filtration been neces- 

 sary. Any excess of the preservative fluid, remaining after the 

 preparation of a certain number of the plates, should be kept on 

 stock (in a dark place), and may be again employed for the 

 same purpose, after filtering and adding a little pure glycerine 

 to counterbalance the accession of a small proportion of nitrate 

 of silver from each successive plate. 



In addition to the glycerine process, we have, at intervals, 

 given some attention to the other means of preserving collodion 

 plates, and have succeeded in attaining that object by several 

 other methods, as also in im})roving the processes already de- 

 tailed in our former coiunmnications. 



