APPARATUS FOR SATURATING WATER WITH SULPHUROUS ACID.

Messrs. A. Boake & Co., of Stratford, London, England, have devised a convenient apparatus for charging water with sulphurous acid which is useful in the making of photographic developers. The following description has been furnished by the firm:

The figure shows one of the siphons connected with a very convenient form of apparatus for preparing a solution of sulphurous acid in water, or of sulphites, as may be required.

The siphons are easy to manage, the flow of gaseous acid being regulated with the greatest nicety by simply turning the milled head shown in the engraving, the liquid acid being gradually converted into gas as the pressure is relieved. There is, moreover, no danger attending the use of this simple apparatus; sulphurous acid exerting at ordinary temperatures a pressure of about 30 pounds on the square inch, while each siphon is carefully tested under a pressure of 200 pounds on the square inch before being sent out.

In preparing a solution, say, of sulphurous acid in water, the ground stopper carrying the tubes for passing the gas should be removed from the glass jar in immediate connection with the siphon, and two-thirds filled with distilled water; the stopper is then to be replaced, and the second glass jar half filled with caustic soda solution. The soda solution is used to absorb any sulphurous acid not dissolved by the distilled water, and so prevent the escape of this irritating gas into the air. Solution of sulphite of soda, and also of bisulphite, can be prepared in a similar way, substituting only pure caustic soda solution for the distilled water employed in the case of preparing the solution of sulphurous acid; but we must rather devise the purchase of the pure solid forms of these salts specially prepared, and put up by us in one-pound stoppered bottles for use in photography; these preparations can be obtained either direct from the manufacturers or from any wholesale chemical firm. The siphons may be obtained either separately or already connected with the absorbing jars. It may be mentioned that these siphons contain about two and a half pounds of liquefied sulphurous acid, and can be refilled when required; but those requiring larger quantities can obtain the acid compound in copper drums.

The Photographic News says: It will be noticed that Messrs. Boake say there is no danger attending the use of the siphons, as the glass vessels are tested at a much greater pressure than that ordinarily exerted by the condensed sulphurous acid; but our readers must remember that a blow against a hard substance may cause the glass to become fractured, and that under these circumstances the bursting of a siphon might cause a serious injury. Still, if proper care is exercised, there need be no accident; but we would suggest that the condensed acid should always be kept in the coolest place available, as the pressure it exerts becomes much greater when the temperature is raised.

The above caution is necessary, as a bare statement that there is no danger may cause persons to handle the siphons without reasonable care. The risk is precisely analogous to that attending the use and handling of bottles containing ordinary aerated waters, only the irritating nature of the sulphurous acid must be taken into account. Instances have occurred in which serious injury has resulted from the bursting of a bottle of soda water; but few, if any, are deterred from the use of soda water or lemonade on this account.

DETERMINATION OF TANNIN.
By E. Johanson.

The precipitation of tannin by a solution of gelatin is effected more completely and in a better condition for filtration if, besides ammonium chloride, as proposed by Schulze and Lehmann, there is also added a small quantity of chromium sulphate or of chrome-alum. The author proceeds in the same manner as Lehmann, but he adds to 100 c.c. of the solution containing sal-ammoniac from 5 to 8 drops of a solution containing 1 part chromium sulphate in 25 parts of water. In order to ascertain the end of the reaction, he filters small quantities into two test glasses of equal width, adds to the one a few drops of a solution of gelatin, observing if the two liquids, when held up against a sheet of black glazed paper, appear opaque or transparent. As long as a precipitate is formed, these portions and the washings of the little filters are poured back to the main quantity. If acetic or tartaric acid is present, the liquid should be neutralized before proceeding to the determination. Johanson points out that, though this method gives good results with the tannin of galls and of oak-bark, an extract of coffee gives no precipitate with solution of gelatin, so that caffeo-tannic acid cannot be determined in this manner. This shows that only quantities of tannin of one and the same kind can be compared with each other.

THE INCOMPLETE COMBUSTION OF GASES.
By Harold B. Dixon, M.A.

[Abstract of a paper read before the Chemistry Section of the British Association at Montreal.]

The author gave a resume of the work he had done in continuation of the researches of Bunsen, E. von Meyer, Horstmann, and other chemists, on the division of oxygen when exploded with excess of hydrogen and carbonic oxide. The following are the general conclusions arrived at:

1. No alteration per saltum occurs in the ratio of the products of combustion. The experiments made completely confirm Horstmann's conclusion; Bunsen's earlier experiments being vitiated by the presence of aqueous vapor in the eudiometer.

2. A dry mixture of carbonic oxide and oxygen does not explode when an electric spark is passed through it. The union of carbonic oxide is effected indirectly by steam. A mere trace of steam renders the admixture of carbonic oxide and oxygen explosive. The steam undergoes a series of alternate reductions and oxidations, acting as a "carrier of oxygen" to the carbonic oxide. With a very small quantity of steam the oxidation of carbonic oxide takes place slowly; as the quantity of steam is increased, the rapidity of explosion increases.

3. When a mixture of dry carbonic oxide and hydrogen is exploded with a quantity of oxygen insufficient for complete combustion, the ratio of the carbonic acid to the steam formed depends upon the shape of the vessel and the pressure under which the gases are fired. By continually increasing the initial pressure, a point is reached where no further increase in the pressure affects the products of the reaction. At and above this critical pressure the result was found to be independent of the length of the column of gases exploded. The larger the quantity of oxygen used, the lower the "critical pressure" was found to be.

4. When dry mixtures of carbonic oxide and hydrogen in varying proportions are exploded above their critical pressures with oxygen insufficient for complete combustion, an equilibrium is established between two opposite chemical changes represented by the equations:

(I.) CO + H₂O = CO₂ + H₂.
(II.) CO₂ + H₂ = CO + H₂O.

At the end of the reaction the product of the carbonic oxide and steam molecules is equal to the product of the carbonic acid and hydrogen molecules multiplied by a coefficient of affinity. This result agrees with Horstmann's conclusion. But Hortsmann considers that the coefficient varies with the relative mass of oxygen taken.

5. A small difference in the initial temperature at which the gases are fired makes a considerable difference in the products of the reaction. This difference is due to the condensation of steam by the sides of the vessel during the explosion, and its consequent removal from the sphere of action during the chemical change. When the gases are exploded at an initial temperature sufficiently high to prevent any condensation of steam during the progress of the reaction, the coefficient of affinity is found to be constant whatever the quantity of oxygen used—provided only the quantity of hydrogen is more than double the quantity of oxygen.

6. The presence of an inert gas, such as nitrogen, by diminishing the intensity of the reaction, favors the formation of carbonic acid in preference to steam. When the hydrogen taken is less than double the oxygen, the excess of oxygen cannot react with any of the three other gases present—carbonic oxide, carbonic acid, and steam—but has to wait until an equal volume of steam is reduced to hydrogen by the carbonic oxide. The excess of inert oxygen has the same effect as inert nitrogen in favoring the formation of carbonic acid. The variations in the coefficient of affinity found by Hortsmann with different quantities of oxygen are due partly to this cause, but chiefly to the varying amounts of steam condensed by the cold eudiometer during the reaction taking place in different experiments.

7. As a general result of these experiments it is shown that, when a mixture of dry carbonic oxide and hydrogen is exploded with oxygen insufficient for complete combustion, at a temperature at which no condensation of steam can take place during the reaction, and at a temperature greater than the critical pressure, an equilibrium between two opposite chemical changes is established, which is independent of the mass of oxygen taken, so long as this quantity is less than half the hydrogen. Within these limits the law of mass is completely verified for the gaseous system composed of carbonic oxide, carbonic acid, hydrogen, and steam at a high temperature.

HERBST'S METHOD OF FILLING.
Demonstrated by Dr. G. C. Cludius, Grenoble, France.[12]

At the July meeting of the Odontological Society of France, Dr. Cludius, from Grenoble, made the following demonstration of a new method of gold filling, saying:

We feel the necessity of making the operation of filling teeth with gold easier, if possible, especially in difficult cases, in order to lessen the fatigue of the operator, as well as to prevent the suffering of the patient, during hours without interruption, under the ceaseless blows of the mallet. The remedy has been sought in new forms of material, like sponge and crystal gold. These have not given any help in the performance of good operations, but have rather facilitated poor work. We are not in need of varieties in the forms of gold, but we ought to try and improve its manipulation, and this has recently been done in a novel manner by Dr. Herbst, whose rotation method has been mentioned in the dental journals within only a few months; and yet it seemed necessary that this great invention, made in Bremen, should take its way by America to come to us.

In the January meeting of the Odontological Society of New York, Dr. Bödecker mentioned it for the first time, describing the excellence of fillings made by Dr. Herbst in less than half the time that any mallet work would have required, and he expressed his intention of going to study the method with the inventor. Thinking that I was yet nearer to Bremen, I went thither, and found there Dr. W. D. Miller, who had come on the same errand. Mr. Brasseur had also written to Dr. Herbst, and it is by his (Mr. B.'s) invitation that I came to Paris to show you what I have learned in Bremen. To-morrow morning I shall show the method in the mouths of patients at the Dental College of France. Dr. Herbst did not patent his new method, to which may be given the name of "rotation gold filling." All he desires is that every one may try the system, and he feels himself already largely paid by the acknowledgments he is daily receiving.

He proves that by his way of rotation one is able to adapt the gold more perfectly to the walls of the cavity than by any other means hitherto employed. One can thus work gold in the very weakest teeth, because there is no force employed, yet the gold is as much condensed as by any mallet known.

The new instruments are very simple, and you may find them in the dental depots. One can easily prepare them for himself—at least the principal one, No. 5—by putting a broken burr in the hand-piece and holding it like a pen for writing until the rotating end of the burr is ground to a roof-like shape, on a dry Arkansas stone. Nos. 1, 2, 3, and 4 are smooth burnishers, and help to fix the first layers of gold in large fillings. They are afterward used as finishers, Nos. 9 to 17 are finishing burnishers, and No. 18 is a needle-point finisher.

The cavity is to be prepared in the usual way, but retaining points are very much less needed than for other methods. Take, for instance, a central cavity in a molar—and, moreover, the fundamental idea of this system is to transform all cavities to be filled into central cavities. Now fix several cylinders, of a size proportioned to the cavity, with a common plugger, and then take No. 2, or 3, or 4, and by a slow rotation polish the gold against the walls. If the gold does not stick directly, put in more cylinders with the plugger, and recommence the condensation with the burnisher. On this first layer of gold a second one is to be made to adhere; but the polished surface prevents, and here No. 5 finds employment in quick rotation and interrupted touches until the polish is gone. (I may here remark that the gold is condensed by this rotation and without pressure in a very remarkable way.) For large fillings, No. 5 is to have proportionate points,[13] which, if too fine, will make holes in the gold, and the pressure is to be intermittent, in order to avoid the development of heat, which would be painful and irritating to the pulp.

All the instruments by use get gilded, and will not work longer without tearing out the gold; but this inconvenience may be prevented by occasionally rubbing them while in rotation upon a piece of tin.

The filling of the cavity is continued in the way above described.

Let us now take the case of two incisors with lateral cavities approximating one another. The two cavities, prepared as usual, are treated as if one, and the gold is at the same time introduced into both cavities, fixing some cylinders in the four corners by rotation of the proper burnishers, and condensation with No. 5, until they are filled, so that there appears to be a single mass of gold. No. 18 is then pushed with regular rotation between the teeth until the mass is quite separated, so that thin files, and disks, and tapes may be employed in finishing the fillings.

In filling similar cavities between the second bicuspid and first molar, after they are properly prepared, place a matrix and fill one cavity with shellac to retain the matrix, and distribute the resistance, and then fill the other like a central cavity, beginning at the cervical border, and pressing especially against the matrix at that point, work toward and finish at the middle of the crown. Having filled the first one, remove the shellac and fill the other in the same way.

The rotation and the pressure, if intermittent, do not produce heat—at least, not more than will render the gold cohesive.

Dr. Herbst filled for me two molars, carious to the cervical border, and very sensitive there, for which reason they had for years been filled with plastics, because I was afraid of perforation if retaining points were made, without which gold filling by malleting would not have been possible; and I was too nervous to sit three or four hours in the chair. Dr. Herbst filled both teeth by rotation, without retaining points, in a little more than one hour. Several gentlemen present have seen them and observed the severe tests to which Mr. Brasseur subjected them, and I may add that notwithstanding the great sensitiveness of the dentine and the proximity of the pulps, I felt not the least inconvenience from heat, and my own patients bear like testimony.

We will now split a crown filled in the hand, and you see that the gold is pressed into the smallest depressions of the interior surface, and is so uniformly condensed as to resemble an ingot, impossible to separate in pieces, yet you may note the different stages of the rotation.

I saw Dr. Herbst fill six cavities—some of them large ones—in front teeth, taking altogether at the same sitting about one hour.

It would be difficult to precisely describe the manipulation requisite for the great variety of cases presenting in practice, but I have explained to you in theory the typical ones in the hope of stimulating you to try this method of filling by rotation, which I look upon as one of the most ingenious modes yet given to our profession. The results are splendid, and the operator will thereby save much time and prevent great suffering on the part of the patient.