52 M. C. Lea—The Latent Photographie Image. 
C. Acids. 
Of a number of organic acids tried with excess of potash, 
one only, cevadic acid, exhibited tolerable developing power. 
Phenol, and glycerie, and gentianie acids powerfully reduced the 
silver haloids, but with little or none of the elective power 
necessary to produce an image. One, oleic, produced an image 
lighter than the ground. Sant nic, sinapic, gummic, malic, and 
seg acids produced either fain traces of an image or none 
nadous acid (potassium vanadite with excess of 
ee failed to exhibit any developing power. 
D. Resins. 
Resinous substances “8 the most part dissolve easily in dilute 
aqueous potash, and exhibit more or less developing power. 
Foremost among them is i seis casi which gives a very vigorous 
image, not far short of what may be obtained with sertantion 
m of tolu and ordinary resin both have moderate develop- 
in veer: Resin scarcely attacks the parts that have not been 
acted upon by light, whereas tolu does so. Resin of podophyl- 
lin gives a strong oe 
E. Essential Oils. 
When oil of cloves is boiled for a few moments with dilute 
aqueous potash, and the mixture is then much diluted with 
water, it acts slowly on the image, but as the action is sustained 
te cle, pre sate ae the ay of about an hour, a vig- 
us a 1 of Roman chamomile acts 
ibaa sides Ayah pie eclly. Oil of peppermint produces 
an image of a i color, and at the same time darkens the parts 
not acted upon by light, thus producing an image on a darker 
round. Something similar has been already mentioned in the 
ae of oleic acid. In these cases, where the light acts, the de- 
veloping agent seems to reduce metallic silver, elsewhere, a dark 
basic salt, pene with organic matter in combination, is formed. 
F. Bases. 
Daturin (atropin?) gives a weak image. Codein, As 
a general thing the organic bases exhibit little laoleaey: to evoke 
the latent image. 
G. Pyrogaliol. 
In the course of this investigation, some interesting and new 
observations were made in connection with this well known 
agent, ais deserve mention here 
gallol is well known to have, when employed by itself, 
i tlerahie developing power, which however, 1s greatly in- 
creased by the presence of caustic or carbonated alkalies. It 
appears that these alkalies can be re laced with sodium mefa- 
phosphate, with about equal results. With sodium hypophosphite, 
