JOURNAL OF CHEMICAL EDUCATION
102
in which weight units are specified. Thus the acetic acid example, based on normality, works out nicely, while the sulfuric acid solution may be shown to be 84.88 per cent rather than 82 per cent. Such an error can have grievous consequences in industrial applications. My purpose is to point out the necessity for specific gravity in this computation and to emphasize its importance in all calculations involving solutions. A surprising number of trained men fail to make the distinction between density and specific gravity and to consider the effect of different test and reference temperatwes. EMERY N. WESCOTT
and correctness of this definition from another textbook: "The critical temperature of a gas is the highest temperature a t which that gas may be converted into a liquid." The examination of twenty-five textbooks of freshman chemistry reveals that twelve authors use the incorrect definition quoted above. It is to be hoped that these authors will pay attention to this topic in future revisions, and that teachers of chemistry will be alert in presenting to their students a clear definition of critical temperature.
M. E. LASH K A N S ASTATE ~ COLLEGE MANHATTAN, &Nsns
ANDOVER. MASSACHWETT~
To the Editor: Your editorial in the November, 1953, issue on the To the Editor: materialistic attitude and poor expressive abilities Neighbor Wescott is quite correct in calling attention to the fact that the problem in question should be solved of our recent college graduates has prompted me to remark about the latter defect. by weight rather than by volume. The lack of ability to read, write, and express ideas The correct solution of the problem follows. can only be traced to a lack of ability t o think. The Problem: If 150 ml. of 95 per cent sulfuric acid is mixed with 50 ml. of 43 per cent acid, what is the per problem is: how can we make them think? As a partial solution to this difficult question, we use a sugcent of acid in the mixture? gestion adapted from Adler's well known treatise, Solution: "How to Read a Book." Briefly, in most laboratory 150 ml. X 1.8337 g./ml. = 275.06 g. of 95% &SO4 reports at most schools it is customary t o require the 50 ml. X 1.3294 g./ml. = 66.47 g. of 43% &SO* writer's description of the experimental procedure in where 1.8337 and 1.3294 are the respective specific detail. Instead of this, we require the student to write in ONE sentence a complete, succinct, almost terse gravities a t 20/4'C. description of the procedure followed. . .and no semi0.95 x - 43 colons or hyphens allowed. \ 7 As a result, the student is forced to reflect a t length, and even sometimes to think, about what he actually did do in following the experimental directions. Needless to say, this is not a complete answer to the problem; and, further, this method possesses one distinct advantage: the report can be graded in less time and with less boredom on the part of the teacher. JAYA. YOUNQ KING'SCOLLEGE WILKES-BARRE. PENNSYLVANIA
T o the Editor: "The temperature above which a gas cannot be liquefied by any pressure is called the critical temperature of that gas." This definition appears in a widely used textbook of college chemistry. Now a moment's consideration shows that it is a false statement, for actually there are hundreds or even thousands of temperatures above which a gas cannot be liquefied by any pressure. The definition emphasizes how a gas cannot be liquefied rather than how it can be liquefied. Notice the clarity
To the Editor: Varshni's empirical rule for orientation of aromatic substitution (J. CHEM.EDUC.,30, 465 (1953)) is essentially equivalent to that of Hoffert (J.Sac. Chem. Ind., 42, 348 (1923)), to whom priority should be acknowledged.
