1864. | Elementary Chemistry. 5638 
for its uses and not yet for its own sake. Ata later stage, when the 
science is an object of interest independently of its applications, some 
account of these is not unnaturally mixed up with its teaching, being 
introduced partly for the sake of illustration, partly to exhibit its 
practical importance. For example, the books of arithmetic now in 
common use, and, we believe, still more those of an earlier date, give 
“rules” for the performance of various commercial calculations, which 
it is no doubt well to teach to those who will have occasion to use 
them, but which should be dissevered from the systematic study of the 
science of number. 
We observe to a much greater degree a similar medley of science 
and its applications in works on Chemistry. We will borrow from 
Dr. Apjohn’s manual a few examples of the kind of useful information 
which appears to us out of place in a scientific treatise. Under the 
head ‘‘ Phosphorus” (p. 889), we find an account of the manufacture 
of lucifer matches; under carbonic acid, a discussion on ventilation, 
and an account of the preparation of aérated drinks (pp. 491-493). 
No less than three-and-twenty pages are devoted to the manufacture, 
purification, and illuminating power of coal-gas. The following ex- 
tract from the chapter on Carbon will serve well to convey our 
meaning :— 
“The diamond is valuable for cutting glass, and its powder is much 
used for cutting and polishing the diamond itself, and the harder 
gems. It is, however, principally employed as an ornament for the 
person ; and is worked by the lapidary into forms whieh have received 
respectively the names of the rose and brilliant. The rose is flat 
below, and is cut above so as to exhibit 24 facets. The form of 
the brilliant is the same ; but it is domed below as well as above, and 
is similarly cut on the two surfaces. When cut and polished, a 
diamond weighing one carat is valued at 8/., and its price augments 
as the square of its weight, until this latter reaches 20 carats ; above 
this weight its price rises in a much quicker ratio.” 
It may be useful to know these facts, but assuredly they have very 
little to do with chemistry. Descriptions of the mode of preparing 
substances on a large scale, and tables for ascertaining the strength of 
an acid from its specific gravity, might also be excluded; the former, 
because they illustrate no chemical principle which an experiment on 
the small scale does not better illustrate ; the latter, because though 
invaluable in a work of reference for laboratory use, they are not 
adapted to be read through or remembered. 
The language of chemistry presents grave difficulties to those who 
are commencing the study, not only because of its lengthy and often 
barbarous character, but because of its ambiguity, one substance 
having frequently a number of names. This want of uniformity 
appears to be a necessary consequence of the rapid progress of the 
science. New ideas require new words, and until they have met with 
general acceptance or rejection, the new and the old words are in use 
together. All that a writer can attempt is to make as consistent a 
selection as possible, balancing the claims, often opposed, of scientific 
accuracy and of usage. Even if usage could be summarily disregarded, 
