346 Andlysh of Scientific Books. 



searches on the laws of heat, and those of Berard and Delaioche. ' We-- 

 may likewise,' say these able chemists, ' deduce from our researches 

 another very important consequence for the peoeral theory of chemical 

 action ; that the quantity of lieat developed at tiie instant of the combination 

 of bodies, has no relation to the capacity of the elements ; and that in the 

 greatest number of cases, this loss of heat is not followed by any diminution 

 in tlie capacity of the compounds formed. Thus, for example, the combi- 

 nation of oxygen and hydrogen, or of sulphur and Icrid, which produces so 

 great a quantity of heat, occasions no greater alteration in the capacity of 

 water, or of sulphuret of lead, than the combination of oxygen with copper, 

 lead, silver, or of sulphur with carbon, produces in the capacities of the 

 oxides of these metals, or of carburet of sulphur.' — ' We conceive, that the 

 relations which we have pointed out between the specific heats of simple 

 bodies, and of those of their compounds, prevent the possibility of suppos- 

 ing, that the heat developed in chemical actions, owes its origin merely to 

 the heat produced by change of state, or to that supposed to be combined 

 with the material molecules.'— .4)i«a/«s de Chimie ct t'liysique, x. 



" Mr. Dalton, in treatingof the constitution of elaslio fluids, lays it down 

 as an axiom, that diminution of volume, is the criterion of phemical affinity 

 being exercised ; and hence maintains, that the atmospheric air is a mere 

 mixture. Thus, also, the extrication of heat from chemical union, has been 

 usually referred to the condensation of volume. The following examples 

 will shew the fallacy of such crude hypotheses. 1. Chlorine and hydrogen 

 mixed, explode by the sunbeam, electric spark, or inflamed taper, with the 

 disengagement of much heat and light ; and the volume of the mixture, 

 which is greatly enlarged at the instant of combination, suffers no conden- 

 sation afterwards. Muriatic acid gas, having the me;m density of its com- 

 ponents, is produced. 2. M'hen one volume of olefiant gas and one of 

 oxygen are detonated together, three and a half gaseous volum.es result, 

 the greater part of the hydrogen remains untouched, and a volume and a 

 half of carbonic oxide is termed, with about 1-lOth of carbonic acid. 3. The 

 following experiments of M. Gay-Lussac on liquid combinations are to the 

 same purpose. 1. A saturated solution of nitrate of ammonia, at the tem- 

 perature of Cl°, and of the density 1.302, was mixed with water in the 

 proportion of 41.05 to 33.70. The temperature of the mixture sank SSfi ; 

 but the density at Ci° was 1.159, while the mean density was only 1.151. 

 2. On adding water to the preceding mixture, in the proportion of 33.64 to 

 S9.28, the temperature sank 3.4°, while the density continued 0.003 above 

 the mean. Other saJine solutions presented the same result, though none 

 to so great a degree. 



" That the internal motions which accompany the change in the mode of 

 combination, independent of change of form, occasion the evolution of heat 

 and light, is evident from the following observations of Berzelius : — In the 

 year 1811, when he was occupied with examining the combinations of anti- 

 mony, he discovered, accidentally, that several metalline antimoniates, 

 when they begin to grow red-hot, exhibit a sudden appearance of fire, and 

 then the temperature again sinks to that of the surrounding combustibles. 

 He made numerous experiments to elucidate the nature of this appearance, 

 and ascertained that the weight of the salt was not altered, antlthat the 

 appearance took place without the presence of oxygen. Before the ap- 

 pearance of fire, these salts are very easily decomposed, but afterwards 

 they are attacked neither by acids nor alkaline leys — a proof that their con- 

 stituents are now held together by a stronger affinity, or that they are more 

 intimately combined. Since that time he has observed these appearjuices 

 in many other bodies, as, for example, in green oxide of chromium, the 

 oxides of tantalum and rhodium. — See Chromicai. 



" Mr. Edmund Davy found, that when a neutral solution of platinum was 

 precipitated by hydro-sulphuret of potash, and the precipitate dried in air 

 deprived of oxygen, a black compound was obtained, which when heated 

 out of the contact of air, gave out sulphur, and some sulphuretted hydrogen 

 gas, while a combustion similar to that in the formation of the metallic 

 snlphurets appeared, and common sulphuret of platinum remained behind. 

 When we heat the oxide of rhodium, obtained from the soda-muriate, 

 water first conies over : and on increasing the temperature, combustion 

 taVes place, oxygen gas is suddenly disengaged, and a suboxide of rho- 

 di^um remains behind. The two last rase.^t are nnalogons to that of the 



