644 
The Progress of Chemical Industry. 
portable form of primary battery, which shall prove of ready appli- 
cation by our miners. Electricity has also placed at the command 
of chemists greater intensity of heat than can be derived from 
ordinary sources. 
The study of heat, irrespective of electricity, has largely reacted 
on chemistry, and while the Bessemer process has entirely revolu- 
tionised the manufacture of steel, and almost annihilated the dis- 
tinction in value between that and other forms of iron, the Siemens 
and other furnaces have led to unprecedented economies in the 
expenditure of fuel, and at the same time have facilitated the appli- 
cation of heat in various chemical processes. In the other direction 
— the absence of heat — Professor Dewar has, during the present 
year, made most important advances. Although air had previously 
been liquefied, he has now been able, by means of intense cold alone, 
to reduce atmospheric air to the liquid condition. His further re- 
sults, by a combination of enormous pressure and extreme cold, are 
well known, and now that oxygen and nitrogen have yielded them- 
selves to the advances of science and have been obtained in quan- 
tities in a liquid state, it is hard to say that hydrogen is destined 
always to remain intractable. What may be the ultimate result of 
the investigations that can now be carried on at temperatures 
ranging from 100° to 200° Centigrade below the freezing point of 
water it is impossible to foresee. From researches already made in 
this country and in France, it would appear that most substances 
under extreme cold are, so to speak, dead, and that their ordinary 
affinities are in abeyance. Possibly what may be termed “ glacial 
chemistry ” may eventually enlarge our views as to the various pro- 
perties of matter. 
As to the advances in our knowledge of the chemistry of light, 
the present condition of photography may testify. When we can 
take the image of a bullet flying at the rate of 3,000 feet per second, 
with its accompanying cone of compressed air ; when we can pro- 
duce photographs which are practically permanent ; and when we 
call in the action of light to engrave our steel or copper-plates and 
to produce efficient substitutes for wood-cuts, we seem to be getting 
near the limits of the practical application of photography. And 
yet many of us may remember the days when the daguerreotype was 
regarded— and justly so — with wonder ; and I can myself call to 
mind a still earlier form of photography, by which natural leaves 
were reproduced on paper sensitised with a salt of silver, of which I 
saw specimens in an exhibition at Dresden so long ago as the year 
1839. 
In the introduction of artificial light much also has been done. 
It is true that Pall Mall was experimentally lighted by gas in 1807, 
but it was not until 1842 that gas found its way into Grosvenor 
Square and some other aristocratic quarters of the metropolis. Since 
that time immense strides have been made in the art of gas 
manufacture, while, in consequence of the waste products arising in 
the process having now found commercial uses, great reductions 
have been made in its cost. At the present time gas has to compete 
