318 Chemical Society: — Mr. Hutchinson on the 



"On the Preparation of Cyanide of Potassium, and its applica- 

 tions," hy Professor Liebigof Giessen. (Inserted in vol. xx. p. 2G5.) 



" On the Specific Heat and Conducting Power of Building Ma- 

 terials," by John Hutchinson, Esq. 



The following is the substance of Mr. Hutchinson's paper : — The 

 author, after mentioning the state of our knowledge respecting the 

 conducting powers for heat of different substances, proceeds to point 

 out an important source of error in all such investigations hitherto 

 made arising from the neglect of correction for differences of specific 

 heat among the bodies examined ; the effects observed being evi- 

 dently mixed effects, arising from both causes. This being the case, 

 before any correct investigation of the relative conducting powers 

 of building materials referred to could be advantageously undertaken, 

 it became indispensable to acquire a previous knowledge of their 

 relative capacities for heat, in order that correction for differences 

 of this kind might be made. This inquiry, therefore, naturally pre- 

 ceding that of the proper subject of the paper, first attracted the 

 author's attention. 



The building materials selected for experiment were the following : 

 — Oak, beech and fir-woods ; common, facing and fire-brick ; As- 

 phalte composition, hair and lime mortar, lath and plaster, Roman 

 cement, plaster and sand, plaster of Paris, Keene's cement ; slate, 

 Yorkshire flag-stone, Lunelle marble, Napoleon marble, Portland 

 and Bath-stone ; and lastly, three specimens of the stones now used 

 in building the Houses of Parliament. 



The plan of experimenting chosen was that known as the " method 

 of mixture," this appearing by all evidence on the subject to be the 

 most unobjectionable. The process followed differed but little from 

 that described by Regnault in his recent researches. A suitable quan- 

 tity of material in fragments being accurately weighed out and placed 

 in a little wire basket with the bulb of a delicate thermometer in the 

 midst, the whole was exposed in au inclosure heated by steam until 

 the thermometer ceased to rise, when the basket was withdrawn and 

 plunged with suitable precautions into a vessel of water at a tempe- 

 rature a little below that of the atmosphere. After the lapse of a 

 very short interval the temperature of the water was carefully ob- 

 served, and its rise gave the means of calculating the specific heat 

 of the substance. 



The author remarks on the necessity of equalizing as much as pos- 

 sible the times of heating of the different substances, having observed 

 a great difference in the results given by the same body when slowly 

 and when quickly raised to the high temperature required for the ex- 

 periment, and attributes this difference to an alteration in the state 

 of the currents or waves of heat travelling inwards towards the centre 

 of the solid. 



A number of minute precautions, indispensable to a correct result, 

 were also pointed out and exemplified. The results of the investiga- 

 tion were given in a tabular form, and the principle of the calculation 

 described. 



With the knowledge thus obtained the author proceeded with his 



