Young — Fajjour-Pressures, Sfc, of Thirt/j Pure Substances. 383 



this substance. Two methods were employed, but neither of them gave very 

 satisfactory results. 



(a) An ethereal solution of isopropyl iodide was treated with sodium, a 

 little water being added^ to promote the action. A considerable amount of 

 propylene was formed and carried away some of the di-isopropyl ; but a suffi- 

 cient quantity of the paraffin was obtained. After removal of the greater part 

 of the ether and unaltered iodide by distillation, the di-isopropyl was treated 

 with strong sulphuric acid; and the pure paraffin was finally purified by 

 fractional distillation througli a five-column " evaporator " still-head. It was 

 collected in two fractions. 



Specific gravity at 074°, . . - . . A = 0-67951 

 „ . . . . ^ = 0-67945 



Boiling-point under normal pressure, 68'1°. 



(b) A strong solution of potassium isobutyrate was electrolyzed in a cell 

 of special construction, Every precaution was used to avoid loss of di-iso- 

 propyl; but under the best conditions the yield was only 1'5 grams from 100 

 grams of isobutyric acid, the theoretical amount being 49 grams. The chief 

 product of the reaction was isopropyl isobutyrate, large quantities of pro- 

 pylene being also formed. The quantity of di-isopropyl obtained by tins 

 method was too small to admit of its complete purification. 



The specific gravity of the small impure specimen obtained by the second 

 method was 0-6806, and on distillation the greater part came over at 58-0°, 

 the temperature finally rising to 58-8°. The first specimen was employed for 

 all the determinations. 



7. Di-isobutijl? — This paraffin can be satisfactorily prepared either by the 

 action of sodium on isobutyl bromide or by the electrolysis of a strong 

 solution of potassium isovalerate. 



The action of sodium on isobutyl bromide is fairly rapid, and there was no 

 difficulty in preparing a sufficient amount of the hydrocarbon. As the boiling- 

 point of di-isobutyl ( i09'2°) is considerably higher than that of isobutyl bromide 

 (92-3°), the paraffin could be separated fairly completely from the unaltered 

 bromide by fractional distillation. The final purification was effected by 

 treatment with a mixture of nitric acid and sulphuric acid, and subsequent 

 fractional distillation through an efficient still-head. 



It is to be noted that pure isobutyl bromide cannot be obtained by 

 distillation, because partial dissociation into isobutyleue and hydrobromic 

 acid takes place ; and the products of dissociation recombine to some extent 

 on cooling with formation of the tertiary bromide. A small quantity of 



' Silva, Beiichte, v., p. 984, 1872. - Fortey and Young, lov. eU. 



3 g2 



