136 
temperature as high as is consistent with the 
attainment of a final temperaure below the critical 
temperature. This is effected by passing the cold 
expanded air at about —140° around tubes sup- 
plied by a T branch from the intake of the 
machine, i.e. with air at go At. and at —100° C. 
It liquefies part of this compressed air, and is 
warmed up thereby to about —130°, at which 
temperature it is admitted to the exchanger. A 
further improvement is obtained, much as in 
multiple expansion steam engines, by expanding 
in stages and warming up the expanded gas in 
between by making it circulate over coils filled 
with air above its critical pressure. 
Thus at the present time liquid air may be pro- 
duced in large machines for an expenditure of 
power perhaps one-fourth to one-fifth of that re- 
quired in the Hampson simple laboratory machine, 
but it must still be regarded as a somewhat ex- 
pensive and troublesome commodity to base a 
process upon. Naturally the question arises how 
it is that such great results may be confidently 
anticipated of its use. It has already displaced 
all other processes for the production of oxygen 
and nitrogen on a large scale, and, in the same 
field, the preparation of pure hydrogen and carbon 
monoxide from water gas offers no insurmount- 
able difficulty. The industry can supply oxygen 
to-day, in plants of 1000 cubic metres per hour, at 
o'2d. per cubic metre, and this means that to 
burn coal in pure oxygen rather than in air would 
increase the cost of the fuel only some four times. 
The saving in certain cases, through not having 
to heat at the same time a mass of nitrogen at 
least two and a half times greater than that of 
the coal and oxygen together, is evident. But 
this to-day’s figure gives no conception of what 
could be done if chemists really set themselves to 
separate the oxygen and nitrogen of the atmo- 
sphere before use, even in such common processes 
as the combustion of fuel. It can be stated con- 
fidently that the cost of the oxygen would not 
exceed that of the coal, without taking into 
account the possible use of the nitrogen produced 
at the same time. When it is considered how all 
industrial chemistry has been based upon the 
necessity of taking oxygen always diluted with 
some five times its volume of nitrogen, the revolu- 
tion in methods that these facts suggest is 
obvious. A blast furnace, for example, consum- 
ing oxygen instead of air, would be very different 
from the present affair. 
The reason why the liquefaction of the atmo- 
sphere and its subsequent rectification holds out 
such great industrial possibilities, in spite of the 
somewhat expensive character of liquid air, is, of 
course, that the cold is used regeneratively. 
There is an apparatus into which air at ordinary 
temperatures passes, and out of which oxygen and 
nitrogen, at a few degrees only from that tem- 
perature, issue. In other words, the losses of 
cold through the issuing gas being at slightly 
lower temperature than the entering gas are so 
small that_in the rectification of thirty litres of 
liquid air into its components some twenty-nine 
litres would be’ recovered. 
NO. 2292, VOL. 92] 
NATURE 
) 
\ 
Actually, there is a } 
[OcTOBER 2, 1913 
very slight expenditure of power required, 
amounting theoretically to o'1 H.P. hour per 
cubic metre of oxygen separated. In addition, 
the losses through heat enfering the well-insu-. 
lated apparatus from outside must be considered, 
but these, naturally, are the smaller the larger the 
scale of operations. The yield of pure oxygen, 
the nitrogen being left with 2°4 per cent. of 
oxygen, per H.P. hour is, for a plant of 50 cubic 
metres per hour, about 1 cubic metre; of 100 
cubic metres per hour, 1°2 cubic metres. For 
larger plants 1°5 cubic metres is confidently pre- 
dicted. For the purpose of the industries fixing 
atmospheric nitrogen, naturally, great purity of 
the nitrogen rather than that of the oxygen is 
aimed at, and in these a purity of 99’9 per cent. 
can be realised, the oxygen testing some 80 per 
cent. 
Space does not permit any detailed discussion 
of the factors which have enabled the older Linde 
process to compete successfully, and now to co- 
operate with, the newer processes utilising the 
principle of external work, though, as admirably 
set forth in this book, these are fascinating 
enough. Nothing less than real genius could 
have enabled Linde eighteen years ago to grasp 
and work out the intrinsic possibilities of success 
in the “internal work” method, which appears 
theoretically to be so barbarously wasteful, or to 
have designed the apparatus which, as Claude 
remarks, strikes one at first sight like a coach 
with five wheels. It furnishes a most interesting 
example, in this region of topsy-turvy thermo- 
dynamics, of how thoroughly the theoretical 
aspect of a problem may change the more deeply 
and completely it is examined. 
(2) The volume by Prof. Marchis is comple- 
mentary to the other, and does not deal with the 
production of the extreme temperatures necessary 
for the liquefaction of air. It gives a most read- 
able and useful account of the science of refrigera- 
tion as applied to the preservation of perishable 
commodities. It is packed full of practical in- 
formation about refrigerating machines and in-: 
sulating materials, the construction and manage- 
ment of cold-storage chambers and ice factories, 
and the preservation of the great variety of comes- 
tibles dealt with nowadays, each of which requires 
its special treatment if the best results are to be 
attained. The book can be confidently recom- 
mended as being in itself almost sufficient for an 
engineer without experience to undertake this 
field of work. At the same time, it contains much 
recent information of general utility to all inter- 
ested in the subject. A description of the recent 
high-speed rotary compressors of M. Leblanc, with 
vanes of ramie fibre, agglutinated by the solution 
of acetate of cellulose in acetone, and running in 
a casing with practically no play at a peripheral 
speed of 500 metres per second, ends an abundantly 
illustrated section dealing with the various types 
of refrigerating machines. In the last two 
chapters the special cases of the preservation of 
meat and of fish are treated in detail. The 
author combats the prevalent idea that cold storage 
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