BETWEEN THE VISCOSITY OF LIQUIDS AND^ THEIR CHEMICAL NATURE. 107 
distillation slackens, the condenser is turned up again, and more sodium introduced ; 
a further quantity of ten or twelve grams can be dissolved in the remaining alcohol. 
An amount of alkyl iodide, three-fourths of that required for the total quantity of 
sodium alcoholate now in the flask, is added as before, and so a second quantity of 
ether obtained. It is possible to continue this process so that the final amounts 
of sodium and alcohol unutilised shall bear as small a proportion to the total ether 
produced as we please, especially if the alcohol obtained by fractionation of the early 
distillates be added to the flask ; but time and the accumulation of sodium iodide 
fix a practical limit. 
The ethers prepared in this way were methyl-propyl, ethyl-propyl, methyl-isobutyl, 
and ethyl-isobutyl. The dipropyl ether was prepared by Krafft’s method, as already 
described. The methyl and ethyl iodides used were prepared by myself. The 
alcohols were obtained from K^hlbaum ; the propyl alcohol boiled between 95°'7 and 
97°'0 (corr.), and the isobutyl alcohol from 106°'4 to 108° (corr.). Each ether was 
repeatedly fractionated in a Lebel-Henxinger apparatus, and the main fraction, after 
frequent and prolonged digestion with sodium wire, boiled within about half a degree. 
It appeared to be practically impossible to obtain an ether which would show abso¬ 
lutely no gas bubbles on the introduction of fresh sodium wire, so one was compelled 
to consider the drying complete when the amount of this trifling action became 
constant on each successive addition of wire. This minute quantity of moisture 
would appear to have no effect upon the viscosity observations, as an ether after 
repeated treatment with phosphoric oxide gave results almost identical with those 
given by the liquid before treatment. (See p. 83.) 
