4M. C. Lea—The Latent Photographie Image. 53 
indicate that they might exhibit power of development al 
Cases they were boiled a few moments with dilute aqueous 
potash, as it was found that in that way their characteristic 
actions were most fully brought out. Aloes, uva ursi leaves, 
areca nuts, the bark of the berberin tree, morus tinctoria, exhib- 
ited very considerable developing power. Gratiola, qpecacuanha, 
pimento nuts, well marked power, but less than the foregoing. 
A decoction of Iceland moss exhibited the properties already 
described in the case of oleic acid and essential oil of pepper- 
mint. Many other substances were examined, and showe 
either faint traces only or absence of power, e. g., litmus, cartha- 
nus, rutin, bryony, stavesacre, colchicum, turmeric, nus: vomica, caffe- 
in, berberin, ete. 
Acetone, in conjunction with aqueous potash, is a powerful 
developer and gives a bold and vigorous Image. 
ldehyde, with potash, gives no image, a result that seems 
somewhat remarkable. 
matters, 
_ When to a solution of cuprous oxide in ammonia, formic acid 
's added in quantity not quite sufficient to neutralize the bases, 
and this solution is applied to the latent image, a powerful 
development is obtained, resulting in a pure black image. 
Lactic acid exhibits a similar reaction, but less perfectly, and 
no doubt a large number of other organic acids share the same 
rties 
pro : 
arious substances that develop in presence of potash, 
especially gum guatacum, gallotannic acid and manna, heighten 
the action of the cupro-ammonia solution. Others do not, of + 
which picrotoxin (coceulus indicus) is an example. Of all the 
substances named, guaiacum appeared to have the most power, 
and next to it, perhaps formic acid. 
J. Ferrous Salts, : 
The salts of ferrous oxide have proved to be the most inter 
esting and remarkable of all the bodies examined, in their 
