the furnace mentioned was shown, also several novelties, among which was the model of the mouth of a Zulu, which had been taken by Mr. Crapper during a visit of the troupe to Hanley; this was useful in demonstrating what well-developed mouths this race possess.

AN ANNOYING ACCIDENT.

"SCHWALBACH," under the above heading, mentions the fact that some flat teeth after being backed and soldered, and as I have experienced, when the piece has been polished, a tooth drops off without any apparent cause. My experience has told me the cause of this evil is not far to seek. No elaborate paragraph on heat and contraction is needed, for the fusion of the solder has nothing to do with it. It is simply a flaw in the platinum wire, which can be seen through a magnifying glass, or by taking a pair of pliers and putting some little strain on the wire, when it will be found to give way.

I remember, when I was an assistant, once having painful experience of this same annoyance, when, not an isolated tooth and that occasionally, but often two at a time came away. I can distinctly recollect six incisors coming away. The teeth, which were new stock, were subjected to examination, and the result was that in the workroom there was no hesitation in saying that it was the wire that was at fault. Should any one have the misfortune to possess a number of such teeth they may be sent back to the depôt. How to repair a tooth which has given way flush with the mineral may be new and interesting to some. Clean the amputated pin, put the tooth into plaster and sand, take a small piece of gold and weld into a round nugget; when done it is as strong as before. Pierce out pins left in the back, and solder in usual way.-W. P. ROBERTSON. Crown Street, Aberdeen.

THE MANUFACTURE OF CELLULOID.

CELLULOID is made by dissolving pyroxyline (or guncotton) in camphor, instead of ether or alcohol. To prepare it for treatment with the camphor it is first ground in water. After the water has drained off, it is placed under pressure

in a perforated vessel, and almost converted into a solid body, which, however, still contains enough moisture to prevent spontaneous ignition in the subsequent operations. This mass is now intimately mixed with camphor by grinding them together in water. One part of camphor, by weight, is employed to two parts of pyroxyline, but other proportions can be employed with good results. The desired pigments and other substances are added along with the camphor. After they have all been very thoroughly mixed, the mass is subjected to a very heavy pressure, which removes all the moisture, and also brings the camphor into more close contact with the pyroxyline to aid it in dissolving the latter. The dried and pressed mass is now put into a vessel of the form in which it is desired to have the celluloid. In the top of this vessel is a piston or plunger, so that it can be subjected to the action of a hydraulic press. While under pressure it is heated by steam or otherwise to from 140° up to 265° F., according to the quantity of the mixture. It is kept at this temperature and under this pressure until the camphor has dissolved all the pyroxyline. The temperature increases the solvent power, while the pressure keeps the ingredients in intimate contact. The result is a solid mass perfectly homogeneous throughout.

Another form of the same material, called artificial ivory, is prepared from 100 parts of ivory dust, 100 of pyroxyline, and 50 of camphor. The pyroxyline is ground wet, then pressed until only enough water remains in it to prevent ignition. It is then mixed with the ivory dust and camphor, and pressed between absorbing cushions until all the moisture is extracted. Then 50 parts of nitrate of ethyl are added. The mixture is then left for several hours in a closed vessel until the nitrate is equally distributed throughout the mass. It is next subjected to heavy pressure in heated cylinders, as before described, and rolled between hot rollers. The product thus obtained has the appearance of natural ivory, is free from streaks and spots, is not attacked by moisture, and while hot can be pressed into any shape.

Celluloid, as it leaves the press, is about as dense as sole leather, but hardens in the air, owing to a slight evaporation of camphor. In the finished product there is still a good deal of camphor, and herein is found the essential advantage in the use of camphor over ether, alcohol, and other liquid or volatile solvents. All such solvents are completely removed from the mass, while enough camphor remains in it perpetually to serve as solvent over and over again, and to give it the property of being readily changed into any other shape

at a high temperature without the addition of any other solvent.

By another process a dilute solution of camphor is employed, one part camphor to eight of alcohol, which will not dissolve pyroxyline at common temperatures, but does so when heated. The pyroxyline is ground, mixed with pigment or dye, the water all removed, and one part of solvent added to two parts of pyroxyline, well stirred and put in a closed vessel until the solvent has saturated all parts of it. It is then heated under pressure as before described. The Compagnie Franco-Americaine, at Stains, near Paris, has been making celluloid for over three years, and has a branch at Mannheim, in Baden. The rubber-comb company in Hanover also took up its manufacture, but abandoned it again owing, it is said, to the danger from fire. Renleaux is of the opinion that some experimenter should contrive a method for dispensing with the camphor, and also rendering the pyroxyline less combustible; two difficult problems which Professor Wagner believes are not likely to be accomplished.

Unlike hard rubber, celluloid does not become electrical when rubbed. The odour of camphor can only be noticed when the substance is warmed, or on being rubbed. The numerous uses to which it is applied are too well known to need repetition here.-Missouri Dental Journal.

Hospital Reports and Case-Book.

MONTHLY REPORT OF CASES TREATED AT THE DENTAL HOSPITAL OF LONDON,

FROM DECEMBER 1ST TO DECEMBER 31ST, 1880.

MONTHLY REPORT OF CASES TREATED AT THE
NATIONAL DENTAL HOSPITAL,

FROM DECEMBER 1ST TO DECEMBER 31st, 1880.

Children under 14

QUARTERLY REPORT OF CASES TREATED AT THE HOSPITAL OF EXETER.

FROM OCTOBER 1ST TO DECEMBER 31ST, 1880.

Extractions Adults

258

568

Miscellaneous Cases (Irregularities of the Teeth, Scaling,

WITHIN a very short time nitrous oxide gas has been the subject of discussion at three different professional gatherings. First, at the meeting of the Midland Counties Branch

of the British Dental Association at Manchester, the late Mr. Henry Marsh read the paper which we published in our number of November 1st. At the November meeting of the Odonto-Chirurgical Society at Edinburgh, Mr. Williamson's paper, going over nearly the same ground, gave rise to an animated discussion, of which we give a brief report in our present issue; whilst, in December, Mr. Lyddon read a very interesting communication before the Odontological Society relating to certain exceptional phenomena which may be produced by the gas.

In the course of these debates the best modes of making, storing, and administering the gas were discussed in considerable detail, so that we need say nothing more on these points; but there is one aspect of the subject which, though incidentally referred to both by Mr. Marsh and Mr. Williamson, and especially dwelt upon by Mr. Geo. Lyddon, has not yet, we think, received quite as much attention at the hands of the profession as is deserves or requires. That nitrous oxide is, as was stated by several speakers, "the safest and best anæsthetic known for minor or short operations," there can be no doubt, but as regards its reliability there has been, we think, too great a tendency to prejudge, and even to pooh-pooh, the question. It may, then, be worth while to inquire, Is nitrous oxide a thoroughly reliable anæsthetic? Can it always be depended on to produce the effects which are expected of it? Or what reason have we to doubt this?

So far as we are at present aware, the reliability of nitrous oxide as an anesthetic was first publicly called in question in a letter which appeared in the Times' of May 18th, 1880, and in which the writer, who signs himself "E. W. B.," declares that, although he had twice inhaled twenty gallons of the gas, he had not on either occasion been in the least affected by it. Several answers to this letter subsequently appeared in the same paper, of which the most satisfactory was by Mr. G. H. Bailey, a gentleman who, as is well known, has had, at the Dental Hospital of London and elsewhere, a very large experience in the use of

gas. Whilst admitting that some persons will take a