TRANSACTIONS OP SECTION A. 537 



the entii-e oxidation of the carbon, and part of the gases escape as carbon monoxide 

 •(CO), with a consequent loss of heat energy, and the measurements are incorrect. 



In the apparatus of Messrs. Favre and Silbermann the gases resulting from 

 the combustion of fuel are deprived of the carbon dioxide and passed over cupric 

 oxide, for the estimation of the weight of carbon monoxide, but even this modifi- 

 cation does not enable an absolutely exact correction to be made. 



Mr. Lewis Thompson designed some time ago an ingenious apparatus, in which 

 he obtained the oxygen for fuel combustion from potassium chlorate and potassium 

 nitrate intimately mixed with the fuel in a finely divided condition : the mixture is 

 ignited with a fuse. 



The dissociation of the potassium chlorate, however, generates heat, and heat 

 is absorbed by the transition of the oxygen from a solid to a gaseous condition ; 

 the dissolution of the residual potassium chloride also absorbs heat, so that con- 

 siderable corrections have to be made. 



Berthelot mentions that in the hands of Stohmann the solid oxygen arrangement 

 has been greatly improved and increased in accuracy. Berthelot and Vieille finally 

 decided to confine themselves to the use of oxygen in a gaseous form as the oxidis- 

 ing agent in their calorimeter. By the use of gaseous oxygen a single difficulty only 

 ias to be overcome — the complete oxidation of the fuel without producing a trace of 

 carbon monoxide or of hydrocarbon. This difficulty is successfully met by com- 

 pressing oxygen to about seven atmospheres, and with a weight of combustible 

 such that the proportion of oxygen consumed does not exceed 30 or 40 per cent, of 

 its total quantity. The air is forced into the small and strongly formed mortar- 

 jahaped vessel by a force-pump. 



The advantages obtained by this new arrangement are that the calorimetric 

 measurement can be performed in from three to four minutes, whUst the actual 

 combustion occupies only a few seconds. A very small quantity of water is required, 

 80 that a high temperature is obtained, thereby increasing the precision. The pro- 

 duct is not found to contain any residual gases, judging from critical analyses. 



The ignition is effected by passing an electric current through a platinum wire 

 and cage (in which the fuel is placed). 



With this instrument Berthelot and Vieille have established the calorific 

 value of the most important pyrogenic hydrocarbon compounds. The results are 

 given in the ' Comptes Rendus ' for May 31, 1886. 



The only disadvantage of this excellent instrument is its cost ; it can be 

 obtained from M. Golas, of Rue St. Jacques, Paris, who makes Berthelot's splendid 

 instruments of precision. 



Mr. W. Thomson, of Manchester, has lately improved the Lewis Thompson 

 calorimeter, employing gaseous in preference to solid oxygen, in a very simple 

 manner, and, as far as the author can judge, the instrument appears the most 

 satisfactory for popular use : the combustion is likely to be slightly incomplete 

 owing to the use of oxygen at atmospheric pressure, but for practical purposes the 

 instrument is all that could be desired. 



The author suggests that the standard marketable value of coal should be ex- 

 pressed in the weight of fuel in decimals of a pound required to raise one pound 

 of water to 212° Fahr. or 100° Centigrade from an initial temperature of ("say) 

 77° Fahr. or 25° Centigrade. 



18. On Secular Experiments in Glasgoiu on the Elasticity of Wires. 

 By J. T. BoTTOMLET, M.A., F.B.S.E. 



The object of this paper is to put on record the state of the wires in the secular 

 ■experiments on stretching of wires commenced under the British Association and 

 with the aid of a money grant. A committee was appointed at the last Glasgow 

 meeting for the purpose of inaugurating these experiments ; and preparations having 

 been made in tlie interval, the wires were set up in 1879. Several reports have 

 been already made to the British Association, and observations are carried on from 

 time to time on the condition of the wires, which are hung up in the Tower of the 

 University Buildings of Glasgow. 



