RICHARDS. — HEATS OF COMBUSTION OF ORGANIC SUBSTANCES. 579 



tals were drained, melted, and then recrystallized, about the first fifth 

 of the crystals being discarded. From the remaining benzol about one 

 third was allowed to crystallize. These crystals were drained, melted, 

 and recrystallized as before, the first crystals being discarded. About 

 one half of the remaining benzol was allowed to crystallize and was 

 retained as the final sample. The freezing-point of this sample was 

 determined in a regular Beckmann fi-eezing-point apparatus, using all 

 of the precautions to prevent supercooling. The freezing-point was 

 found to remain constant until practically all of the sample tested was 

 frozen, thus indicating its purity. Especial care was taken to keep 

 these preparations free fi-om dust and other impurities, both during 

 and after the purification. 



The thermochemical results showed that these two samples were 

 essentially the same, as far as the present purpose was concerned. 



The Combustion of Sugar, 



The details of conducting a combustion of sugar in the calorimetric 

 bomb in the adiabatic calorimeter are easily told. 



About 1.5 grams of sugar were accurately weighed in the platinum 

 crucible in which the substance to be burned was placed. The sugar 

 was not compressed into tablets, as has been the custom of previous 

 investigators, but was burned as a powder. This method is the less 

 troublesome and also the safer one, in that it involves less manipulation 

 of the substance ; moreover, in a preliminary series of experiments it 

 was found that powdered sugar and sugar tablets gave perfectly con- 

 cordant results. 



The platinum crucible was placed m its support, a platinum ring 

 secured to one of two stout platinum wires projecting downward from 

 the cover of the bomb. These wires formed the terminals of an electric 

 circuit. A spiral of very fine iron wire to serve as the igniter was sus- 

 pended between them, dipping into the crucible and buried in the 

 sugar. A small amount of water, never more than a milliliter, was 

 sprayed into the bomb, so that the space might be saturated with 

 water- vapor, in order to avoid a correction for the evaporation of part 

 of the water formed by the combustion. The cover was then placed 

 on the bomb, and a gas-tight joint was made by means of the screw- 

 cap fitting over it. Oxygen was run into the bomb until it was under 

 a pressure of 35 atmospheres. This high pressure was always used, in 

 order to be more certain of obtaining complete combustion, unless 

 otherwise indicated. 



Meanwhile the rest of the apparatus was being prepared. The dilute 

 alkaline solution in the jacket and cover was brought to a temperature 



