LETTERS dar Weights-Absc
dative?
To the Editor: I enjoyed reading the letter from Thomas B. Coolidge which appeared in the March issue of the JOURNAL OF CHEMICAL EDUCATION, but feel that additional comment is necessary. I agree with Professor Coolidge that clearly defined terms consisting of properly assigned numerical values and precise dimensions are of great importance in the study of chemistry or of any other science. However, I do not agree that his definition of molecular weight is the only definition or necessarily the best. A good definition should be as fundamental as possible, and should not rely on any particular 'system of physical dimensions. To my mind there are two meanings to the term "molecular weight," and we should differentiate them as follows: 1. Absolute molecular weight or the mass of an individual molecule. 2. Relative molecular weight or a relationship hetween masses of equal numbers of molecules. I would like to state my concept of relative molecular weight by the following definition: If n M , is the mass of n molecules of a substance A, and nMo, is the mass of n molecules of diatomic oxygen, then the relative molecular weight of A, rMA,is given by
is a relative number which furnishes a correspondence between masses of equal numbers of molecules. A convenient unit of mass used in chemical calculations is the mass mol or, as it is generally called, the weight mol or weight molecular weight. If U, is the unit of mass employed, the mass mol of a substance A, MMA, would be defined by MMA 5 U,rMa
Dimensions [Mass]
It has been concluded from experimental evidence that for any choice of a mass unit, such as gram, pound, ton, etc., the mass mol consists of a definite (not arbitrary) number of molecules. This number, which I shall designate by N U m , furnishes us with a connecting link between relative molecular weight and absolute molecular weight. If aM* is the absolute molecular weight, then MM* = D MA = Nu,
Nu,
Dimensions [ M w ]
The definitions given above certainly work, and I feel that they are clear and precise. WESLEYE. BRITTW U N I V E R ~ ~ TOP Y COLORADO
BOULDER. Co~onnno
Adventures of Kekulb-Brooklyn
Style
To the Editor: In my class in organic chemistry there is a boy with where 32 is an arbitrary but convenient dimensionless a very fine sense of humor, and he is not going to let the austere subject of organic get him down. unit. On a term test the other day, the class was asked to From the above definition, it is apparent that relative molecular weight is neither a mass nor a weight, but discuss "The Benzene Problem." This student's rMA 3 32nMa/nMq
[Dimensionless]
answer to that is clever enough so that I thought you could use it in the "TOURNAL.
high-school chemistry might be partially due to the following.: 1. Lack of concern on the part of the A. C. S. for the "By the benzene problem is usually meant the problem of benzene. Whereas books have been written on this subject high-school teacher, his welfare, and his teaching con(among these the work of Schnoud and the excellent dissertation ditions. Chemistry is being taught in too many schools of Ebbing and Stahfen are recommended to the sincere student) by teachers who are not properly prepared, and in I will confine myself t o a few golden words. laboratories (or without laboratories) that are not "Ya see, de trouble is, wot yuh gonna do wit de unsaturated linkaees. - . hub? ~f vou make her a straieht-~hain-iob.. den properly equipped. The A. C. S. could bring pressure you're nonplussed c& she donat react witupoimanganate, not to raise the professional level and improve the condieven coincentrated, see? So dis guy Kekule he's sleepin' off a tions of the high-school teacher of chemis*. This had one, see, and he dreams up dis ring idea, and he pops it down done, will come in. on paper and den goes out like a light. Well, when he wakes up 2. More could be offered for the benefit of highin de morning he swears he'll never touch anudder drop, see, school teachers in the publications of the A. C. s. specially after he takes a squint a t dat crazy ring he drew de 3. The A. C. S. should do more missionary work to n k h t before. 'Why,' says he, 'anybody dat uose anyting uose dat dere make these non-member teachers of chemistry aware ain't no isomers of meta-dichlorobenzene, dere's only one.' of values available in the A. C. S. publications and "And so, jest t o forget about de whole ting, he kicks de gong aroun' again, and dat's when he dreams up de ascillatin' bonds. membership. As a teacher in a small school where my duties range see, and when he sees wot he's done de next morning he goes t o his liker closet and trows away a whole lot of Scotch, see. Well, from high-class janitor work through Civilian Pilot you asked for her; dere she is, in a nutshell." Training to the teaching of chemistry, I can underThat seems to sum up the benzene prohlem very stand the difficulty of digging up the membership dues each year, but I can testify that the publications and adequately. the pride of membership do produce ample returns in CROOM BEATTY,111 teaching results. ROLLINS COLLEGE
''
WINTERPARK, FLORIDA
Three1
To the Edibr: Editor's note: There has been no "lack of concern on This is to register my interest in both your "Editor's the part of the A. C. S. for the high-school teacher"; Outlook" and "Origin and Transformation of Carbo- rather has there been a feeling that little or nothing can hydrates in Plants," as carried in your January issue. be done about the present conditions. The result of a As a member of the American Chemical Society and a careful study of this matter by a committee of the teacher of chemistry on both the high-school and Council of the Society was published in the News Edijunior college level the following comments may be of tion of Industrial and Engineering Chemistry, 14, 147 some interest. (April 20, 1936). Copies of this report can be had from Low membership in the A. C. S. among teachers of the Secretary of the Society.
