TRANSACTIONS OF THE SECTIONS. 



61 



out that the success of the method depends upon an important condition, which is 

 entirely his own. The ice to be melted must be prepared witli water free from 

 air, and must surround the som-ce of heat in the form of a solid cylinder frozen 

 artificially in situ. Those who have worked on the subject of heat know how dif- 

 ficult it is to measure absolute quantities with certainty, even where relative 

 results of great accuracy may be attained. The ice-calorimeter of Bunsen will 

 therefore be welcomed as an important addition to our means of research. Bunsen 

 has applied liis method to determine the specific heats of ruthenium, calcium, and 

 indium, aud finds that the atomic weight of indium must be increased by one half 

 in order to bring it into conformity with the law of Diilong and Petit. He has 

 also made a new determination of the density of ice, which he finds to be 0-9167_. 



In a report on the Heat of Combination, which was made to this Association in 

 1849, the existence of a group of isothermal bases was pointed out. " As sonre of 

 the bases" (potash, soda, baryta, strontia), it was remarked, "form what we may 

 perhaps designate an isothermal group, such bases wiU develope the same or nearly 

 the same heat in combining with an acid, and no heat will be disengaged during 

 their mutual displacements. Tlie latest experiments of Thomsen have given a 

 remarkable extension to this group of isothermal bases. He finds that the hydrates 

 of lithium, thallium, calcium, and magnesium produce, when all con-ections are 

 made, the same amount of heat, on being neutralized by sulphuric acid, as the four 

 bases before mentioned. The hydrate of tetramethylammonium belongs to the 

 same class of bases. Ethylamin, on the other hand, agi-ees -with ammonia, which, 

 as has been long known, gives out less heat in combining with the acids than 

 potash or soda. An elaborate investigation of the amount of heat evolved in the 

 combustion of coal of difi'erent kinds has been made by Scheurer-Kestner and 

 Meusnier, accompanied by analyses of the coal. Coal rich in carbon and hydi-ogen 

 disengages more heat in burning than coal in which those elements are partially 

 replaced by oxygen. After deducting the cinders, the heat produced by the com- 

 bustion of 1 gramme of coal variedfrom 8215 to 9022 units. 



Tyndall has given an extended account of his experiments on the action of a 

 beam of strong light on certain vapours. He finds that there is a marked dif- 

 ference in the absorbing-power of different vapours for the actinic rays. Thus 

 nitrite of amyl in the state of .vapour absorbs rapidlj' the rays of light competent 

 to decompose it, while iodide of allyl in the same state allows them freely to pass. 

 MoiTen has continued these experiments in the south of France, and among other 

 results he finds that sulphurous acid is decomposed by the solar beam. 



Eoscoe has prosecuted the photo-chemical investigations which Bunsen and he 

 began some years ago. For altitudes above 10 degrees, the relation between the 

 sun's altitude aud the chemical intensity of light is represented by a straight line. 

 Till the sun has reached an altitude of about 20 degrees, the chemical action pro- 

 duced by diffused daylight exceeds that of the direct sunlio-ht ; the two actions 

 are then balanced ; and at higher elevations the direct sunlight is superior to the 

 diffused light. The supposed inferiority of the chemical action of liglit under a 

 tropical sun to its action in higher latitudes proves to be a mistake. According to 

 lloscoe and Thorpe, the chemical intensity of light at Para under the equator in 

 the month of April is more than three times greater than at Kew in the month of 

 August. 



Hunter has given a great extension to the earlier experiments of Saussure on the 

 absorptive power of charcoal for gases. Cocoanut-charcoal, according to Hunter's 

 experiments, exceeds all other Tarieties of wood-charcoal in absorptive power, 

 taking up at ordinary pressures 170 volumes of ammonia and 69 of carbonic acid. 

 Methylic alcohol is more largely absorbed than any other vapour at temperatures 

 from 90° to 127° ; but at 159° the absorption of ordinary alcohol exceeds it. 

 Cocoanut-charcoal absorbs forty-four times its volume of the vapour of water at 

 127°. The absorptive power is increased by pressure. 



Last year two new processes for improving the manufacture of chlorine attracted 

 the attention of the Section : one of these has already proved to be a success ; and 

 I am glad to be able to state that Mr. Deacon has recently overcome certain diffi- 

 culties in his method, and has obtained a complete absorption of the chlorine. 

 May we hope to see oxygen prepared by a cheap and continuous process from 



