16 'I III-: COMPRESSIBILITY OF LITHIUM, SODIUM, 



lacking, the matter was not pursued further. Only a gram and a half of 

 the metal were at our disposal ; but the treatment of this small amount was 

 facilitated by the fact that the large quantity of potassium present liquefied 

 it. The specific gravity of the liquid alloy was found to be 1.285, by 

 means of a tiny pycnometer filled with kerosene, the metal being handled 

 b}' a fine pipette filled with hydrogen. Assuming no contraction upon the 

 formation of the alloy and having given the density of potassium and that 

 of pure rubidium (1.53), it is easy to calculate that about two-thirds of 

 the liquid must have been rubidium. This assumption is only a very 

 approximate one ; but it is supported by the density 0.89 of the liquid alloy 

 of sodium and potassium combined in atomic proportions.* It serves in. 

 the present case because the compressibilities of potassium and rubidium 

 are not very far apart, and therefore considerable uncertainty in the 

 amount of potassium does not greatly affect the result. The trace of 

 sodium which also existed in the metal was too small an amount to cause 

 appreciable error. 



CAESIUM. 



The salt used for the preparation of this metal was purified according to 

 the method of H. L. Wells by repeated precipitation as the dichloriodide. 

 It was as pure as that used in the recent Harvard work upon the atomic 

 weight of the metal. The sulphate was made from it, and then the 

 hydroxide with the help of pure crystallized baric hydroxide. This was 

 dried and fused, and ignited in an iron tube with powdered magnesium in 

 a current of dry hydrogen. The metal which distilled over was collected 

 in a vessel filled with hydrogen, and was transferred in the liquid state by 

 small pipettes filled with hydrogen. The density of a similar but subse- 

 quently made specimen at 20 (in the solid state) was found by Brink to 

 be about 1.87. No analysis of this specimen was made, but it must have 

 been free from all impurities except traces of magnesium and such other 

 impurities as the magnesium may have contained. Rubidium prepared in 

 the same way was found by Brink to contain only insignificant amounts of 

 magnesium and the merest trace of iron. 



PARAFFIN OIL. 



After many experiments upon liquids suitable for conveying the press- 

 ure to the metals, paraffin oil was found to be the only suitable substance. 

 For the preliminary experiments a viscous, very high boiling paraffin 

 lubricating oil was used, after having been purified by long contact with 



*F. N. Brink made experiments on this point also, as will be shown in another 

 paper. He, moreover, made long afterward an approximate quantitative analysis of 

 the particular alloy of rubidium in question, confirming essentially this conclusion. 



