14 THE ATTAINMENT OF VERY LOW TEMPERATURES 



innocuous. I have observed that when using an air Hquefier, and using 

 certain kinds of oil to lubricate the compressor, the vacuum vessel in 

 which the liquid air is collected, when the latter is evaporated, contains 

 a trace of oil. 



After an experiment with a hydrogen Hquefier, the moisture which 

 remains in the vacuum vessel has often an oily smell. I have also often 

 detected the odor of arsenuated hydrogen emitted from the solid con- 

 densed in the vacuum vessel as the apparatus becomes warm. I may 

 say that I have always obtained the best results by using pure zinc, 

 pure dilute sulphuric acid with a little copper sulphate, and taking care 

 to employ a good lubricating oil on the working part of the compressor. 



In June, 1903, I was invited to give a demonstration of the lique- 

 faction of hydrogen before the Congress of Applied Chemistry in Ber- 

 lin. I was unable to obtain a compressor, but was supplied with a 

 number of cylinders of hydrogen, prepared by the electrolysis of cal- 

 cium chloride solution, and compressed to no atmospheres. Six of 

 the cylinders were at once connected with the Hquefier and the ex- 

 panded hydrogen was allowed to escape into the atmosphere. 



Analysis of a sample of this gas showed that it contained 0.2 per 

 cent, of oxygen. There was, however, no tendency for solid to form 

 at the expansion valve and the result of my experiment was the most 

 satisfactory that I ever reached. 



i 



