with the ingenious improvements that have been made in it by Mr. Fischli, assistant to Prof.  Weil, of Zurich.  I have employed it frequently, and I use it every year in my lectures.  I find it very practical, provided one has got accustomed to using it.  It is, at all events, of much simpler manipulation than that of Bertin-Sans, although the accuracy of the latter may be greater (Figs. 3, 4, 5, and 6).  But it certainly has more than one defect, and some of the faults that have been found with it are quite serious.  The worst of these consists in the difficulty of catching the exact moment at which the turbidity of the basic liquid is at the proper point for arresting the operation.  In addition to this capital defect, it is regrettable that it is necessary to shake the flask that contains the solution after every insufflation of air, and also that the play of the valves soon becomes imperfect.  Finally, Mr. Wolpert rightly sees one serious drawback to the use of baryta in an apparatus that has to be employed in schools, among children, and that is that this substance is poisonous.  This gentleman therefore replaces the solution of baryta by water saturated with lime, which costs almost nothing, and the preparation of which is exceedingly simple.  Moreover, it is a harmless agent.

The apparatus consists of two parts.  The first of these is a glass tube closed at one end, and 12 cm. in length by 12 mm. in diameter.  Its bottom is of porcelain, and bears on its inner surface the date 1882 in black characters.  Above, and at the level that corresponds to a volume of three cubic centimeters, there is a black line which serves as an invariable datum point.  A rubber bulb of twenty-eight cubic centimeters capacity is fixed to a tube which reaches its bottom, and is flanged at the other extremity (Fig. 7).

The operation is as follows: 

The saturated, but limpid, solution of lime is poured into the first tube up to the black mark, the tube of the air bulb is introduced into the lime water in such a way that its orifice shall be in perfect contact with the bottom of the other tube, and then, while the bulb is held between the fore and middle fingers of the upturned hand, one presses slowly with the thumb upon its bottom so as to expel all the air that it contains.  This air enters the lime-water bubble by bubble.  After this the tube is removed from the water, and the bulb is allowed to fill with air, and the same maneuver is again gone through with.  This is repeated until the figures 1882, looked at from above, cease to be clearly visible, and disappear entirely after the contents of the tube have been vigorously shaken.

The measures are such that the turbidity supervenes at once if the air in the bulb contains twenty thousandths of CO_{2}.  If it becomes necessary to inject the contents of the bulb into the water twice, it is clear that the proportion is only ten thousandths; and if it requires ten injections the air contains ten times less CO_{2} than that having twenty thousandths, or only two per cent.  A table that accompanies the apparatus has been constructed upon this basis, and does away with the necessity of making calculations.