RICHARDS. — HEATS OF COMBUSTION OF ORGANIC SUBSTANCES. 577 



of the gasket and force out the sides. Some of the lead at the inner edge 

 was then cut away as shown in the diagram. Small strips | | of 



sheet gold, previously annealed, were inserted around this edge so that 

 they might overlap, after which the top was again screwed down several 

 times in order to wedge in the strips of sheet gold. The gold was 

 then bent back over the lead and the top screwed down in order to 

 smooth out the gold lining. A lining of this sort proved entirely 

 satisfactory, though in time a very slight oxidation of the lead occurred, 

 due to the loosening of several of the gold strips. This oxidization was, 

 however, too slight to affect the results, for when a new lining replaced 

 the old, no variation in the results could be detected. 



Instead of the shallow dish ordinarily used for holding the sub- 

 stance to be burned, a platinum crucible (K) weighing about 15 grams 

 was substituted. The platinum crucible has probably several advan- 

 tages over a shallow dish, especially in the combustion of liquids. 

 The high sides of the crucible tend to prevent loss by projection of 

 the material, and the heat at the moment of ignition is probably con- 

 centrated, thus securing a more comjjlete combustion. 



The thermometer (L) was made by Fuess after the ordinary Beck- 

 mann model, with a large bulb containing about 75 grams of mer- 

 cury and possessing a wide and very freely moving thread of mercury. 

 It had been standardized by the Prussian Physikalisch-Technische 

 Reichsanstalt and was subsequently compared here with a most care- 

 fully constructed Baudin thermometer, and with another similarly 

 standardized Beckmann thermometer. All measurements were made 

 over about the same part of the scale, in order to make the results with 

 benzol as closely comparable as possible to the results with sugar. 



The oxygen used was similar to that used by Atwater, and was 

 obtained already compressed in steel cylinders from the White Dental 

 Company of Boston. In order to insure a certain standard of purity 

 in the oxygen, samples of each cylinder were analyzed volumetrically 

 for oxygen, and check combustions were frequently performed with 

 sugar. As a rule, this oxygen contained between 2.7 and 3.2 per cent 

 of nitrogen and no chlorine. In work at present in prospect, it is pro- 

 posed to prepare purer samples of the gas. The effect of the impu- 

 rity of nitrogen is discussed in detail below. 



Purification of Material. 



Cane-Sugar, C10H22O11. Three samples of sugar, designated A, B, 

 and C, were used in this investigation. The source of each sample 

 was the crystallized sugar or "rock-candy" of commerce. For the 

 first, called Sample A, powdered " rock-candy " was dissolved in boil- 



VOL. XLII. 37 



