SCIENCE. 



321 



THE USE OF WATER AS A FUEL. 

 By Dr. George W. Rachel. 



The results of certain experiments, made with what 

 has been called the Holland Hydrogen Locomotive, have 

 lately been published in several city papers. They are 

 not only of the highest practical importance, but of great 

 scientific interest, so that it appears entirely proper to 

 discuss them from that aspect in this journal. 



The fuel used is naphtha and water ; the manner in 

 which combustion is accomplished by a peculiar unique 

 apparatus may be shortly described thus : 



The principal feature of this new invention is an iron 

 retort having two compartments, one for naphtha and 

 the other for water. The two fluids are conducted into 

 the two chambers by induct-pipes at one end of the re- 

 tort, while at the opposite side there are two escape-pipes, 

 through which the vapors of the two substances escape 

 from their respective chambers, where gasification has 

 taken place. The two gases are being mixed by passing 

 into a common receptacle, the manifold, and from there 

 they are distributed through three main pipes to the 352 

 burners. Of these 44 are placed directly under the (four) 

 retorts, while the balance is arranged under the boiler. 



The astonishing results obtained by this ingenious ap- 

 paratus have been the subject of many discussions in 

 various scientific and industrial journals on both sides of 

 the Atlantic. The attacks have usually been directed 

 against the possibility of making an advantageous use of 

 the hydrogen for the purpose of combustion. The ex- 

 planation that in the Holland retort the principal source 

 of the tremendous heat produced, is due to the combus- 

 tion of hydrogen derived from the dissociation of the 

 water vapor, has been supposed to be met by the follow- 

 ing statement : 



The dissociation of the steam must consume as much 

 heat, as is afterward developed by the combustion of 

 the hydrogen. 



It was contended that the principle of the Holland 

 method was entirely wrong, implying an error against the 

 law of the conservation of energy which is the funda- 

 mental law of the Universe, and therefore this whole 

 matter must be a delusion. 



This objection, which looks plausible enough can be 

 shown to be erroneous, as it is based on a misconception, 

 or rather a misinterpretation of this great law of Nature. 

 The error consists in the wrong application of the word 

 heat ; the sentence containing the objection to be correct, 

 must read thus : 



The dissociation of the steam must require as much 

 energy, as is afterward developed by the combustion of 

 the hydrogen thus obtained. Now, it is a fact, that the 

 energy developed by the combustion of the hydrogen in- 

 variably takes the form of heat, but the principle of the 

 correlation of forces which forms the basis of this very 

 law, teaches us that it must not necessarily do so during 

 the process of dissociation. In order to fully expose the 

 misinterpretation of Nature's fundamental law contained 

 in the objection above quoted, we may be allowed a few 

 words on the subject of dissociation. 



Prof. H. St. Clair Deville, who first succeeded in an 

 ingeniously contrived apparatus to dissociate water vapor 

 into its elements, hydrogen and oxygen, estimates the tem- 

 perature required for the purpose at 6ooo v C, probably 

 even somewhere near 8ooo°C. Prof. Schroeder van 

 Der Kolk even places it at a still higher figure, viz.: about 

 io,ooo°C. But these figures, it must be well understood, 

 refer to the dissociation of water vapor in the absence of 

 any other element. If, on the contrary, the dissociation 

 is induced to take place in the presence of other elements 

 — notably metals— the dissociation temperature is low- 

 ered considerably. Thus, for instance, the dissociation is 

 effected in the presence of platinum, at i7oo°C ; iron 

 filings, i4oo°C; silver, iooo p C, instead of 8ooo°C. 



The question is now : How are we account for this ? 



Prof. Deville in a controversy now going on between 

 Prof. Ad. Wurtz and his school, and Berthelot and 

 himself, on this very subject of dissociation, replies to 

 some objections of his adversaries, as follows :* 



It is a well-established fact that the dissociation of 

 water-vapor takes place at much lower temperatures in 



the presence of certain elements These and other 



examples .... prove that the development of heat dur- 

 ing the formation of a compound body, does not hold any 

 known relation to its dissociation temperature. Evidently 

 the error is very frequently committed in regard to these 

 processes to confound actual and kinetic energy, actual 

 and latent heat." 



The relation referred to in this passage, must, how- 

 ever, in the light of the law of "Conservation of Energy" 

 be one of absolute equivalency ; the energy expended on 

 one process — dissociation — must under all circumstances 

 be equivalent to the energy developed during the other 

 process — formation of the compound body, t. e. in our 

 case water-vapor. 



If, therefore, our experiments show that the tempera- 

 ture of dissociation is lowered in the presence of certain 

 elements, we must look for some other form of energy 

 which supplants the amount of heat saved. What force 

 is it that steps in here and plays the role of a dissociat- 

 ing agent in place of the tremendous heat ? The 

 answer is obvious, it is chemical affifiity, for chemical 

 affinity is the only form of energy capable of such intensity 

 of action. Furthermore, chemical affinity is to a certain 

 extent not directly discernible and measurable, as 

 Friedrich Mohr has shown.f 



The irrefutable proof for our assertion lies in the fact 

 that there is in the case under consideration, always 

 formed an oxide of the metal employed. We find the 

 molten silver and platinum CQvered with thin films of 

 their respective oxides while the iron filings show an 

 amount of oxidation which is — as it is in the two former 

 cases — in direct proportion to the quantity of vapor dis- 

 sociated. The chemical affinity of the glowing and mol- 

 ten metals to the oxygen of the water-vapor being greater 

 than the chemical affinity of hydrogen to oxygen, they 

 appropriate the oxygen of the steam, and, combining 

 with it, form their respective oxides — thus liberating the 

 hydrogen and accomplishing dissociation. 



Deville's above-quoted statement, that there is no 

 known relation betweenthe formation — and dissociation- 

 temperatures of compound bodies must be modified, 

 therefore, in the light of the foregoing observations. 

 What he is pleased to call " Kinetic energy " and "latent 

 heat" is actually nothing else than chemical affinity. 

 The position of Wurtz and his followers, by the way, 

 is untenable ; they contend that the two temperatures 

 should be equal, (in accordance with the law of the conser- 

 vation of energy) and meet the often observed fact that 

 these temperatures differ considerably with the assertion 

 that, as theoretically they should not do so, the observa- 

 tions are wrong. Their interpretation of the great prin- 

 ciple contains the same error which the objections to the 

 Holland process are suffering from ; they insist that the 

 energy which produces dissociation must take the form 

 of heat and heat only, because heat is the only form of 

 energy met with during formation. They forget that 

 such limited application of this great principle is entirely 

 arbitrary and that the only requirement of the law is ihat 

 of absolute equivalency, while there is no rule as to the 

 kind of energy required. 



I have been somewhat elaborate in my remarks on 

 the subject of dissociation, because the conditions under 

 which the dissociation of steam ta''es place in the Hol- 

 land process are the exact counterpart to those which 

 have just been dwelled upon. Instead of the metals, the 



*Comptes rendus, 1879. 

 t Science Vol. 1,'pg. 244. 



