Chkmical and Photographic Section, JSTov. 9th.— 
Dr. W. B. Herapath F.R.S., in the chair. Tho attendance was 
very limited, and it was agreed to make the hour of meeting 
eight o'clock. Mr. W. L, Carpenter made a communication 
oa some Analyses of Silicates of Soda. The author referred to 
the want of definiteuess in thecompraunda of silicic acid with 
soda, and the impossibility of isolating them, as they had no 
tendency' to crystallise. He mentioned one which he believed 
to be detinite, as lie had obtained it by two entirely ditiereut 
processes, and adduced the results of many analyses to show 
that the greater the proportion of the acid to the base in these 
salts the more water was necessary to make a solution which 
would not be decomposed by further concentration. Mr. P, 
J. Worsley then read a paper on the Conditions of Sensibility 
of Iodide of Silver. He said that this substance, the one of 
all others most sensitive to light, might be presented to its 
action under two conditions, as nearl^?^ pure as possible, or in 
I conjunction with other substances. In the first case, colour 
and temperature had very little influence, but molecular 
arrangement rnoreso, and unfortunately these physical difJer- 
ences were the least understood. It was exceedingly 
difficult to prepare a pure iodide of silver, even by 
the direct union of its constituents, but a long series of 
experiments led to the conclusion that the salt, if absolutely 
pure, was insensitive. It certainly was not decomposed by 
light, but it was necessary to distinguish between decomposi- 
tion and mere molecular alteration, unaccompanied by 
chemical change. lod. silver occurred in practice in two 
states, a bright yellow, very sensitive, and a pale yellow, in- 
sensitive, or nearly so, to the action of light. When used in 
conjunction with other bodies, its sensibility might be 
diminished, unaltered, or increased. Strong acids, led. 
potassium, and anything 4hat hindered the reducing action, 
I diminished its 8ensibilitj% Of bodies that had no action, the 
author instanced pure water, neutral salts of the alkalies, 
collodion, &c. The most important bodies, however, were 
chose which increased the sensibility, and they varied greatly 
in chemical composition and mode of action. Foremost 
among them were the oxygen salts of silver, also the chloride 
and bromide of silver— then ta.«min,gelatine,gum, sugar, benzol, 
turpentine vapour, and many others. Nearly the whole of 
these could be shown to be themselves decomposable by 
light, air being present also, and the author stated that, as 
far as his experience went, there was no case in which iod. 
silver was sensitive, unless some other substance was present 
which was also reducible by light. Might not the function 
of the iod. silver be, therefore, he said, more mechanical 
than chemical, this salt acting as a kind of filter to separate 
the chemical rays, and concentrate them upon the other sub- 
stance, which was thus more affected by light than it would 
be alone V 
lioTANicAL Section, Oct. 21st. — First evening meeting, 
Mr. Leipner, president, in the chair. It was resolved that 
the meetings for the future should be held on Thursdays, 
instead of Fridays •, also that a Herbarium, which should be 
open to any member of the Parent Society, should be estab- 
lished by the joint efforts of the members of this section. 
Mr. Yabbicom proposed a resolution, urging on the Council 
of the Societj' the desirability of forming a library of 
standard scientific works, especially those whose price placed 
them beyond the reach of individual expenditure. The chair 
having been taken by Mr. Derham, Mr. Leipner read a paper 
on the preparation of some of the lower orders of the vege- 
table kingdom for microscopic observation. Confining his 
I remarks chiefly to the tribe Diatomacea), the author stated 
that the neighbourhood of Bristol contained a great number 
of species, and that they were to be found in abundance in 
almost every part of the Floating-harbour, either attached 
to other objects — as grass, wood, or lilaments of aigce— or 
perfectly free. In the latter condition, Pleurosigna hippo- 
campus and Nitryschia tania might be seen on a bright day 
in greenish yellow masses on the mud outside Cumberland- 
