212 



SCIENCE. 



[Vol. VI., No. 136. 



He would insist on his pupils mastering the princi- 

 ples of stoichiometry, and in working, as far as 

 possible, quantitatively, even in general chemistry. 

 Mr. C. L. Mees heartily indorsed the ideas advanced by 

 Professor Mabery. For three hundred dollars, a good 

 practical chemical laboratory could be established in 

 high schools, which, if properly conducted, would 

 result in great good. He would insist on a student 

 repeating his work until it was exact. No careless 

 work should be allowed. Mr. C. W. Kolbe gave an 

 illustration of high-school instruction in chemistry, 

 which was evidently purely bookish. The young 

 man who had passed a brilliant examination in stoi- 

 chiometry failed to do the simplest kind of a problem 

 afterwards, because, he said, ' it was not in the book.' 

 Miss L. J. Martin thought cliemistry sliould be taught 

 in high schools so as to make the pupils think, and 

 not become mere machines. Prof. O. C. Johnson 

 gave an amusing account of the failure to develop the 

 sense perceptions, which he thought should be an 

 important part of laboratory instruction. Messrs. 

 Bennett, Sheppard, Smith, and the acting vice-presi- 

 dent, Lupton, also took part in the discussion. 



The second subject discussed was, 'To what ex- 

 tent is the knowledge of molecular physics necessary 

 for one who would teach theoretical chemistry ? 



Prof. J. W. Langley was invited to open the dis- 

 cussion on this topic. He gave a very clear and sat- 

 isfactory exposition of the dependence of chemistry 

 upon physics, and of their close relation to one an- 

 other. He drew attention to the fact, that only 

 under fixed or limited ranges of physical conditions 

 do the ordinarily accepted reactions and chemical 

 affinities manifest themselves. Professors Prescott 

 and Lupton took part in the discussion, showing the 

 advisability of delaying any attempts to teach the 

 higher branches of physics until the student had ad- 

 vanced well in practical laboratory work. 



THE SECOND LA W OF THERMO- 

 DYNAMICS.^ 



The second law of thermodynamics has been 

 chosen for the subject of this address : what that law 

 is will be the main question, and tlie ground will be 

 taken that Eankine's view of the subject is the cor- 

 rect one. After calling attention to the statements 

 of Tait and others as to this law, and as to Rankine's 

 way of stating it, no apology will be necessary for the 

 choice of a question which ought already to have 

 been fully and satisfactorily settled. 



There are three different statements, each claiming 

 to be tbe second law of thermodynamics. I. Ran- 

 kine's law : "If the total actual heat of a homoge- 

 neous and uniformly hot substance be conceived to 

 be divided into any number of equal parts, the effects 



1 Abstract of an address delivered before the section of me- 

 chanical science of the American association for the advance- 

 ment of science, at Ann Arbor, Aug. 26, by Prof. J. Burkitt 

 Webb of Ithaca, N.Y., vice-president of the section. For the 

 complete address, see Van Js^ostrand's eng. mag., October, 1885. 



of those parts in causing work to be performed are 

 equal." Rankine gives also a second form of the law, 

 in which the expression * absolute temperate ' takes 

 the place of ' total actual heat.' II. Clausius gives 

 as the 'Second fundamental principle,' "Heat can- 

 not of itself flow from a colder to a warmer body." 

 This may be a law in the general theory of heat, but 

 not in thermodynamics, wliich treats of the relations 

 between lieat and mechanical energy; and it has 

 nothing to do with Rankine's law, except as all natu- 

 ral phenomena may be connected. III. The formula 

 for the maximum efficiency of a heat-engine is given 

 as the second law, but this is only a consequence of 

 that law, and the form of the engine. 



It would seem from this variety of statement, that 

 a law of nature might be any thing to suit our pur- 

 pose. I think, however, that a careful examination 

 of Rankine's second law will show that it is genuine, 

 and that it is not universally quoted only because it 

 is not understood. Rankine's law is either copied ver- 

 batim, or modified in a way to make this evident; 

 and I must confess, that, before working upon the 

 subject myself, I had difficulty with Rankine's state- 

 ments: they seem now, however, so reasonable, that 

 I shall endeavor to lead you to the same opinion. 



Let us see now what is most natural and appropri- 

 ate for a second law: the first law states that heat 

 and work are mutually convertible, and convertible 

 in a fixed ratio; and it is appropriate that the second 

 law should state the agency by which such conver- 

 sion may be accomplished, and the rate at which it 

 may be effected. 



A quantity of heat, W, may be employed as an in- 

 strument for the conversion of another quantity of 

 heat, W, into work, or for the conversion of a quan- 

 tity of work, A, into heat; and the converted quantity 

 will be proportional to the converter quantity for a 

 given change of volume or of entropy. 



To realize the truth of this statement, let us im- 

 agine the simplest physical air-engine: we need no 

 fly-wheel, valves, etc., but simply a vertical cylinder 

 of infinite height, and unit section, with non-conduct- 

 ing walls, the bottom permeable to heat, and the non- 

 conducting piston loaded with a pressure varying so 

 as to be always equal to the gaseous pressure beneath 

 it. 



But this is no more than the shell of the engine: 

 we will suppose the piston at such a point that the 

 cylinder shall have a volume of one cubic unit; and 

 we must now put in it, say, one unit of mass of the 

 molecules of a perfect gas, resting on the bottom as 

 dust, or distributed through the space as in any gas, 

 but devoid of motion : we have now added the mus- 

 cles, but they are dead flesh ; the engine is not capa- 

 ble of transforming heat into work, or vice versa. The 

 agent by which such a transformation maybe accom- 

 plished is not present; the space through which the 

 piston may move exists, but the molecules exert no 

 pressure against the piston, and there can be no ques- 

 tion of work until we have both space and pressure. 

 To obtain this necessary pressure we must heat the gas 

 to the absolute temperature, r; i.e., we must store in 

 the molecules an amount of kinetic energy propor- 



