Chemical Science. 181 



by any other means. He also remarks, that in consequence of this 

 circumstance, and thes mall quantity of zinc requisite to produce the 

 effect, it may frequently happen that whilst analyzing gases over 

 mercury, when solution of potash is used to absorb carbonic acid 

 gas, errors may be introduced from the evolution of hydrogen. 

 Another observation is, that mercury, through which hydrogen gas 

 from zinc had passed, had dissolved zinc and obtained the power 

 of absorbing oxygen from the air; and that with such rapidity as to 

 suggest the notion that an amalgam of a small quantity of zinc 

 might even serve some useful eudiometrical purposes. — Gio. de 

 Fisica, vii. 238. 



22. Coating for Specula. — An amalgam of two parts of mercury, 

 one of bismuth, one of lead, and one of tin, is sometimes used to 

 cover one surface of blown glass, or glass of any form, so as to 

 make it a mirror. An inconvenience, connected with the use of 

 this substance in experiments or otherwise, results from the con- 

 stant fluidity of the metallic surface, so that it is easily displaced. 

 M. F. Lancellotti having occasion to make experiments of this 

 kind, was induced to search for some other alloy for the productioa 

 of these reflecting surfaces He found that a compound of three 

 parts of lead and two of mercury, fused, and thrown with a certain 

 degree of quickness and dexterity over the clean dry surface of the 

 hot glass, formed a metallic coat which adhered firmly to the glass. 

 It is requisite that the glass should be uniformly heated, and that 

 it should also cool uniformly ; and that after the amalgam is fused, 

 its surface should be perfectly cleaned from any powder or oxide. — 

 Gio, de Fisica, vii. 132. 



23. Caslorina, anew animal substance — The following substance 

 is described by M, Bizio in the Giornale de Fisica, vii. 174. Some 

 castor was boiled in six times its weight of alcohol, 0.85, the liquor 

 filtered when hot and set aside for two or three days, gradually 

 deposited a substance which had no regular form, was extremely 

 light, and fell into powder under the fingers. Alkalies had no 

 action on this substance, when their solutions were boiled on it, 

 except to remove colouring matter and thus render it purer. It 

 was but slightly soluble in cold alcohol, more, as has been seen, in hot 

 alcohol : cold water scarcely dissolved any of it, hot water took up 

 a small portion. The cold solution in alcohol, when spontaneously 

 evaporated, gave the substance in small prismatic acicular crystals, 

 some lines in length, diaphanous and white. It dissolves in ether 

 very readily. When heatud it fuses and appears to boil, vapours 

 arise from it, which in the open air burn brilliantly ; in close vessels 

 it gave the usual products of a vegetable substance, nothing occur- 

 ring to indicate its animal origin. 



24. Strength of Chloride of Lime, or Bleaching Powder, '-The fol- 



