186 ANNUAl. OF SCIENTIFIC DISCOVERY. 



the same, but their pvopertios, both pliysioal and chemical, are 

 extremely tlilVcrcnt. This is a jjood case of kenomerism. Afjain, 

 esseiiee of terebeiilhine combines with liydrochloriLr arid under 

 dilTerent conditions tf) form two distinct hydrochlorates, the 

 monohydrochlorate, C-« Hia II CI, and the diiiyodrocidorate, C20 

 IIio 2 II CI. From the first body tiie crystalline compound C-'" Hie, 

 canij)hen(', is obtained, and from tlie latter C^-n IIin, terpilene two 

 hyilrocarbons of very ilillercnt properties. — Header. 



MECHANICAL ENERGY OF CHEMICAL ACTIONS. 



A supfn^estive paper, by Dr. A^an der Kolk, on the mechnnical 

 energy of chemical actions, appeared in " l\)gu;endorfl"\s Anna- 

 len" some time since. Mr. Foster gives a translation of this 

 l)aper. adding some critical notes in the April number of the 

 " I'liilosoplucal Magazine.*' Dr. Van der Kolk endeavors to show 

 that there is a connection between the experiments of Deville on 

 dissociation, and those of Favre and Silliermann on evolution, 

 and. in a few cases, al)sori)tion, of heat by chemical comljinatiou. 

 Starting from the point tiiat every sul)stance raised to a certain 

 temperature al)ove zero has I'eeeived a given amount of heat, or, 

 as termed i\v Thomson, contains a delinite quantity of energy, 

 the author ))roceeds to examine the different cases presented in 

 chemical union, when the Ijody, after combination, jjossesses 

 either more or less energy than its constituents. He thus arrives 

 at the following law : Bodies which evolve heat, when decom- 

 posed l»y eli'vation of temperature, are not reproduced by subse- 

 quent cooling. Interesting examples conlirniing this law are 

 quoted from Favre and Silbermann's results, from which a second 

 theorem is established, namely, that when a body on heating 

 passes from one condition to another with evolution of heat, it 

 does not return to its first condition upon subsequent cooling; 

 plastic sulphur, barley-sugar, phos])horus, etc., follow this law. 

 The converse to this theorem, though not proved, yet is shown to 

 be frequently confirmed. From these laws it is stated that, in 

 order to produce a chemical compound, not only must there be 

 the chemical force or allinity sullicient for combination, Ijut there 

 must also exist the necessaiy energy. To illustrate this, exam- 

 ples are adduced of phenomena which have hitherto stood as 

 enigmas in chemical science. Thus the electric spark, it is known, 

 can cause the combination of an unlimited quantity of some gases, 

 as, e. 5^., oxygen and hydrogen, whilst other gaseous mixtures 

 can only be graduallv comliined along the path of the spark itself, 

 as, e. g., nitrogen and oxygen. In the first case, the energy of 

 the constituents exceeds that of the compound ; combination of 

 the mass therefore occurs as soon as the power of affinity is In- 

 creased by the spark ; the union of a few atoms of hydrogen and 

 oxygen developing sufficient heat to cause others to coml)ine, and 

 thus of the rest. In the second case, however, as the energy of 

 the constituents is less than that of the compound, the electric 

 spark has not only to increase the affinity, but at the same time to 

 add the needful energy. Hence, as no heat is evolved by the 



