that it will not be properly distributed. Experienced pheasant
and poultry breeders state that by the use of this once a week, gapes are
effectually prevented. In this case, also, I shall be glad to learn the
result if tried.

STEPHEN BEALE.

H----, Eng., Aug. 1.

--_Country Gentleman_.

* * * * *

WOLPERT'S METHOD OF ESTIMATING THE AMOUNT OF CARBONIC ACID IN THE AIR.

There is a large number of processes and apparatus for estimating the
amount of carbonic acid in the air. Some of them, such as those of
Regnault, Reiset, the Montsouris observers (Fig. 1), and Brand, are
accurate analytical instruments, and consequently quite delicate, and not
easily manipulated by hygienists of middling experience. Others are less
complicated, and also less exact, but still require quite a troublesome
manipulation--such, for example, as the process of Pettenkofer, as modified
by Fodor, that of Hesse, etc.

[Illustration: APPARATUS FOR ESTIMATING THE CARBONIC ACID OF THE AIR.
FIG. 1.--Montsouris Apparatus. FIG. 2.--Smith's Minimetric Apparatus. FIG.
3.--Bertin-Sans Apparatus. FIG. 4.--Bubbling Glass. FIG. 5.--Pipette. FIG.
6.--Arrangement of the U-shaped Tube. FIG. 7.--Wolpert's Apparatus.]

Hygienists have for some years striven to obtain some very simple apparatus
(rather as an indicator than an analytical instrument) that should permit
it to be quickly ascertained whether the degree of impurity of a place was
incompatible with health, and in what proportion it was so. It is from such
efforts that have resulted the processes of Messrs. Smith. Lunge,
Bertin-Sans, and the apparatus of Prof. Wolpert (Fig. 7).

It is of the highest interest to ascertain the proportion of carbonic acid
in the air, and especially in that of inhabited places, since up to the
present this is the best means of finding out how much the air that we are
breathing is polluted, and whether there is sufficient ventilation or not.
Experiment has, in fact, demonstrated that carbonic acid increases in the
air of inhabited rooms in the same way as do those organic matters which
are difficult of direct estimation. Although a few ten-thousandths more of
carbonic acid in our air cannot of themselves endanger us, yet they have on
another hand a baneful significance, and, indeed, the majority of
hygienists will not tolerate more than six ten-millionths of this element
in the air of dwellings, and some of them not more than five