136 NEW RESEARCHES ON LIQUID AIR. 



refrigerating plant now in use have not been published, simply because 

 changes are constantly being made in the apparatus. Science derives 

 no benefit from the description of transitional apparatus when there is 

 no secret about the working process and how to carry it into effect. 

 The Philosophical Magazine of February, 1895, contains a fantastic 

 claim put forward by Professor Olszewski, of Cracow, that because he 

 used in 1890 a steel tube combined with a stopcock to draw off liquid 

 oxygen he had taught the world, to use his own language, "the 

 method of getting large quantities of liquid gases." In addition the 

 professor alleges, four years after the event, that the experiments made 

 at the Eoyal Institution are chiefly borrowed from Cracow, and that he 

 is entitled to the credit of all low-temperature research. As to such 

 claims, one can only wonder at the meager additions to knowledge that 

 in our time are unhesitatingly brought forward as original, and more 

 especially that scientific men could be got to give them any currency 

 in this country. Such persons should read the late Professor Wro- 

 blewski's pamphlet entitled "Comment l'air a ete liquefie," 1 and make 

 themselves generally acquainted with the work of this most remarkable 

 man before coming to hasty conclusions on claims of priority brought 

 forward by his sometime colleague. 



Liquefying apparatus. — A laboratory apparatus for the production of 

 liquid oxygen and other gases is represented in section in Plate II. With 

 this simple machine 100 cc. of liquid oxygen can readily be obtained, 

 the cooling agent being carbon dioxide, at the temperature of — 79°. 

 If liquid air has to be made by this apparatus, then the carbonic acid 

 must be kept under exhaustion of about 1 inch of mercury pressure, so 

 as to begin with a temperature of — 115°. Under such conditions the 

 yield of the liquid gases is much greater. The gaseous oxygen, cooled 

 before expansion by passing through a spiral of copper tube immersed 

 in solid carbon dioxide, passes through a fine-screw stopcock under a 

 pressure of 100 atmospheres, and thence backward over the coils of 

 pipe. The liquid oxygen begins to drop in about a quarter of an hour 

 from starting. The general arrangement of the circuits will be easily 

 understood from the sectional drawing. The pressure in the oxygen 

 cylinders at starting is generally about 150 atmospheres, and the best 

 results are got by working down to about 100. If a small compressor 

 is combined with the apparatus, the liquefaction can go on contin- 

 uously. This little apparatus will enable liquid oxygen or air to be 

 used for demonstration and research in all laboratories. 



Vacuum vessels. — It has been shown in previous papers 2 that a good 

 exhaustion reduces the influx of heat to one-fifth part of what is con- 

 veyed when the annular space in such double walled vacuum vessels is 

 filled with air. If the interior walls are silvered, or excess of mercury 



1 Paris, Librairie du Luxembourg, 1885. 



2 "On liquid atmospheric air/' Proc. Roy. Inst., 1893; "Scientific uses of liquid 

 air," ibid., 1894. 



