EVOLUTION OF GASES FROM HOMOGENEODS LIQUIDS. 287 



77(e Formic Acid or Formate used. 



In tlie earlier experiments a solution of a known weight of sodium formate, either 

 5 or TO gram, in a given volume of water was used; after the effect of the finely 

 <li vided particles had been observed, the solution was always filtered into the 

 sulphuric acid. Provided that the solution dropped through the filter at a sufficiently 

 slow rate, and the flask containing the acid was kept constantly stirred, the rise of 

 temperature caused by the admixture of the solution with the already previously 

 diluted acid was not great enough to produce any sensible evolution of gas. In later 

 experiments formic acid was used ; this was prepared according to the method 

 proposed by LORIN, viz., by the dry distillation of equi-molecular parts of dry sodium 

 formate and dehydrated oxalic acid. The acid thus obtained was redistilled, when it 

 boiled uniformly at 107; it contained 76*42 per cent, formic acid. It is thus of the 

 same composition and boiling-point as the rather ill-defined hydrate HCOOH.OHg, 

 which boils at 107'l and contains 77 per cent, of the anhydrous acid. Of this, 

 10 c.c. of a solution containing 3'08 grams of formic acid in 100 c.c. were taken 

 for each set of experiments. 



The Sulphuric Acid. 



Pure redistilled sulphuric acid was heated in quantities of 1 to 2 litres at a time 

 in a large flask until white fumes began to appear, so as to boil off any dissolved air, 

 and to completely destroy any oxidisable material, which might reduce in the course 

 of the investigations the sulphuric acid into sulphurous oxide. The acid was diluted 

 with a suitable proportion of water, the details of which will be given for each series 

 of observations ; and the amount of sulphuric acid per unit volume in these diluted 

 acids was determined either by taking its specific gravity or by precipitation with 

 barium chloride, or in most cases by both methods. 



The apparatus (fig. 1) consisted of a flask (A) of about half a litre capacity, within 

 which was blown a bulb (B) of nearly a quarter of a litre capacity, the space between 

 them being completely filled with olive oil. The upper end of the larger flask was closed 

 with a caoutchouc plug (P), through the centre of which the neck of the bulb passed, 

 while through a side hole in the cork passed a smaller piece of tubing (T), bent twice 

 at right angles, the upper end of which was connected with a burette (Q) ; through 

 another side hole passed a piece of capillary tubing (F), bent twice in a U form. The 

 lower bend of the U was filled with mercury, while at the end furthest removed from 

 the flask was constructed in miniature a gas regulator (R) of the form originally devised 

 by Mr. HARCOURT. The neck of the bulb was closed with a caoutchouc plug, through 

 which the long-range thermometer passed, while a side piece of glass fused on served 

 to connect with the delivery tube. The whole arrangement was enclosed within a 

 double-cased air bath, not represented in the figure, heated by a gas flame issuing 

 from a small jet ; the flow of gas was regulated by a governor. 



