Miscellaneous. 361 
heated with a small quantity of oxide of zinc in order 
to neutralize any excess of acid in the chloride, and then 
filtered through a piece of fine cambric to remove the super- 
abundant oxide. To separate the chloride of zinc, from 
the solution of silk, M. Persoz has recourse to Professor 
Graham’s method of dialysis. The apparatus for dialysis, 
which is a kind of sieve, is made by meaus of a broad strip 
of gutta-percha, bent round and cemented in the form of a 
cylinder, at one end of which is fixed a disc of parchment 
to form the bottom. The apparatus is floated upon a ves- 
sel of water, and the silk solution, previously diluted with 
water to the consistency of collodion, is poured into it. The 
chloride of zinc percolates through the moistened disc of 
parchment, and mixes with the water in which the appa- 
ratus is floating. Ina few days the whole of the chloride 
of zinc will be found to have become separated from the 
silk solution, but the presence of a slight quantity of the 
chloride in the material is of no great consequence, as it 
merely gives rise to the formation, in the sensitive film, of 
a minute quantity of chloride of silver. Although M. 
Persoz does not mention the fact, there is no doubt that a 
dry film of this substance would be quite insoluble in 
water. Its employment is very simple. It is first iodized 
by mixing with it an aqueous solution of iodide, and then 
dried and sensitized ; the exposure and development are 
conducted in the ordinary manner.— Fournal of the Society 
of Arts. 
THE fifth of the Christmas juvenile lectures at the Royal 
Institution, on “ Gases,” was delivered by Professor Frank- 
land, F.R.S. He explained that the words “combustibles 
and “incombustible,” as commonly applied to different cir- 
stances, convey erroneous ideas. For instance, in the com- 
bustion of common gas, intense chemical action, giving out 
heat and light, takes place at the line of contact between 
the gas and common air. It is therefore commonly said 
that the gas is combustible, and the air a supporter of com- 
bustion. But if a room be filled with coal gas, and pipes 
conveying common air be laid on, the air would burn in 
such an atmospheae, just-like what is called inflammable 
gas. The lecturer took a large glass tube about three 
inches in diameter, and fourteen inches long, and plugged 
the lower end of it with a bung, through which passed a 
small glass tube, to admit common gas into the larger one. 
-A second tube, open at both ends, passing through the bung 
admitted a very small quantity of common air, which was 
