4 
action, and probably stimulate the cells of the pigment membrane to 
secrete their molecular pigment from the venous flexuses of the choroid. 
The paper was illustrated by a large number of beautiful drawings, by 
specimens from the Institution Museum, and by numerous microscopic 
anatomical preparations. 
In thanking Dr. Fripp for his exhaustive paper, the President remarked 
upon the profound thought and the condensation of a large amount of 
observation displayed in it, and spoke of the honour thus reflected upon 
the society, as well as of the highest credit being due to the author. 
Mr. W. L. Carpenter, the Hon. Reporting Secretary, then read two 
short communications, the first having reference to Pharoah's Serpents' 
Eggs, the chemical toy now so common, and gave the results of experi- 
ments that he had made to ascertain the composition of the serpent. As 
was well known, the white powder forming the egg was sulphocyanide of 
mercury, and the author described several modes of preparing it. Theo- 
retically represented by the formula H ff C y S 2 it would contain 63.3 per 
cent, of mercury, and the specimen he analysed yielded 64.9 per cent. 
The loss of weight on burning was 19.27 per cent., and as the product 
contained 70.5 per cent, of mercury, it followed that about one-seventh of 
the mercury in the egg was volatilised. On this account he insisted strongly 
on the danger of burning them in small rooms with little ventilation, and 
alluded to the ill effects which had been observed by himself and others to 
arise from so doing. He mentioned the insidious and distressing symptoms 
of poisoning by mercury vapour, and described what he believed to be the 
reason of the fantastic forms and extraordinary increase of bulk sustained 
by the sulphocyanide of mercury when decomposed by heat. He showed 
an experiment to prove that the serpent form was not, as was generally 
supposed, caused by the cone of tinfoil, and described others which led 
him to believe that the blackness of the inside of the serpent was due to 
the mechanical mixture of sulphide of mercury with mellon, or melam, 
products of the decomposition of the sulphocyanides which had been 
studied by Liebig. The brown exterior contained no sulphide of mercury, 
and, when treated with nitro-hydrochloric acid, yielded a solution in which 
sulphuretted hydrogen caused a yellow floculent precipitate, the nature of 
which he had not ascertained. The specific gravity of the serpent was 
0.069, water being 1.000, and such was the continuity of the skin that no 
air escaped through it when the serpent was sunk in water. 
The author's second communication was entitled " Note upon the Artifi- 
cial Formation of Flint." After briefly alluding to the various natural 
deposits of silica, and the nature of some of the compounds of silicic 
acid, Mr. Carpenter said that in decomposing on a large scale a solution 
of silicate of soda by a mineral acid, on one occasion, the silica which was 
