252 
POPULAR SCIENCE REVIEW. 
CHEMISTRY. 
I. Pure Chemistry. — Although no very striking discovery has been made 
in this department of science during the last few months, many subjects of 
minor interest have been investigated, and results obtained which are of con- 
siderable value to the student of science. Foremost among these must be 
placed the researches of M. Stas upon the atomic weights. The experiments 
embodied in Iris paper have occupied several years ; their object being to test 
the accuracy of the hypothesis that all the atomic weights of the elements are 
multiples of that of hydrogen. The complete memoir is, perhaps, the most 
important chemical paper which has ever been written ; and in respect to the 
very ingenious processes devised by the author for avoiding all chance of error, 
the enormous labour attending the purification of the materials used, or the 
almost fabulous accuracy of the results when compared one with another, 
these researches of Stas will always be regarded as a masterpiece of analytical 
research. Were the memoir confined to the abstruse scientific point, the 
decision of which it has for its object, a more than passing notice of it would 
be out of place in the pages of a popular review of science ; but, like 
many other investigations by a real master in science, the incidental mat- 
ters touched upon are of the greatest interest and value to practical men. 
Stas is the first who has set to work in earnest to prepare absolutely pure 
materials on a tolerably large scale, and in this he has been beset -with so 
many unexpected difficulties, that it is not too much to affirm that perfect 
chemical purity is a thing hitherto unknown. He gives the most minute 
instructions for the preparation of absolutely pure hydrochloric, nitric, and 
sulphuric acids, water, ammonia, chloride of sodium and potassium ; metallic 
silver and lead ; and by the careful details which he gives on this subject, 
and also by his tests for ascertaining the presence of impurity in any 
of the above chemicals, Stas has conferred a lasting benefit upon all 
scientific inquirers. Already we find that he has raised the standard of so- 
called purity in several manufacturing works, whilst photographers, as well 
as practical chemists, are applying his processes for the preparation of 
metallic silver and its nitrate for their own purposes. As a result of this 
laborious investigation, Stas has been led to the conclusion that there is no 
numerical relation whatever between the atomic weights of elementary 
bodies. 
Dr. Andrews has published the results which he has obtained on exposing 
the non-condensable gases to the combined action of great pressure and low 
temperature. By employing the elastic force of the gases evolved in the 
galvanic decomposition of water as the compressing agent, he succeeded in 
reducing oxygen gas to ^-J-o-th of its volume at the ordinary temperature of the 
atmosphere, and subsequently effected the same object by mechanical means. 
The gases, when compressed, were always obtained in the capillary end of thick 
glass tubes, so that any change they might undergo could, be observed. The 
pressures applied were only limited by the capability of the glass tubes to 
resist them, and, as a further means of effecting condensation, the gases were 
exposed, in their highly compressed state, to the action of a freezing mixture, 
which would reduce their temperature to - 106° Fahrenheit. By this means, 
