Saturday, April 12, 2008

Late 19th century science suppliments--Scientific American

Scientific American Suppliments from the late 19th Century are available online from Project Gutenberg. Good reading of a bygone era and some fine illustrations.

Here is a sample:

Scientific American Supplement. Vol. XVIII, No. 460.
Scientific American established 1845.
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.


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.


APPARATUS FOR ESTIMATING THE CARBONIC ACID OF THE AIR. 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 ten-millionths.

Carbonic acid readily betrays its presence through solutions of the alkaline earths such as baryta and chalk, in which its passage produces an insoluble carbonate, and consequently makes the liquid turbid. If, then, one has prepared a solution of baryta or lime, of which a certain volume is made turbid by the passage of a likewise known volume of CO2, it will be easy to ascertain how much CO2 a certain air contains, from the volume of the latter that it will be necessary to pass through the basic solution in order to obtain the amount of turbidity that has been taken as a standard. The problem consists in determining the minimum of air required to make the known solution turbid. Hence the name "minimetric estimation," that has been given to this process. Prof. Lescoeur has had the goodness to construct for me a Smith's minimetric apparatus (Fig. 2) 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 CO2. 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 CO2 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.

An air that contained ten thousandths of CO2, or even five, would be almost as deleterious, in my opinion, as one of two per cent. It is of no account, then, to know the proportions intermediate to these round numbers. Yet it is possible, if the case requires it, to obtain an indication between two consecutive figures of the scale by means of another bulb whose capacity is only half that of the preceding. Thus, two injections of the large bulb, followed by one of the small, or two and a half injections, correspond to a richness of 8 thousandths of CO2; and 5½ to 3.6 thousandths. This half-bulb serves likewise for another purpose. From the moment that the large bulb makes the lime-water turbid with an air containing two per cent. of CO2, it is clear that the small one can cause the same turbidity only with air twice richer in CO2, i.e., of four per cent.

This apparatus, although it makes no pretensions to extreme accuracy, is capable of giving valuable information. The table that accompanies it is arranged for a temperature of 17° and a pressure of 740 mm. But different meteorological conditions do not materially alter the results. Thus, with 10° less it would require thirty-one injections instead of thirty, and CO2 would be 0.64 per 1,000 instead of 0.66; and with 10° more, thirty injections instead of thirty one.

The apparatus is contained in a box that likewise holds a bottle of lime-water sufficient for a dozen analyses, the table of proportions of CO2, and the apparatus for cleaning the tubes. The entire affair is small enough to be carried in the pocket.—J. Arnould, in Science et Nature.

Scientific American Suppliments

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