MECHANICS AND USEFUL ARTS. 91 



water which is to be used into a minute aqueous dust or dew, just as we see 

 a high wind do with the water issuing from the jets of a fountain. This 

 dew is driven into the box through an aperture on a level with the knees; and 

 owing to the extreme minuteness of its particles, the latter ascend, and then 

 gradually subside on the body. In a short time these particles coalesce and 

 trickle down the body, until at last the water descends in an unceasing 

 stream. This system has now been tried with great success at the Hopital 

 St. Louis, and is generally attracting the attention of medical men. 



LIQUID GLUE. 



As long ago as 18-32, Dumoulin published a notice in the Comptes Rendus 

 of the French Academy with reference to the preparation of a liquid glue. 

 He was led to the discovery of a method of procuring it by considering the 

 long-known fact that Avhen solution of glue is frequently heated and cooled, 

 or kept a long time exposed to heat, it loses its property of gelatinizing by 

 cooling, and remains liquid. Under the impression that this change might 

 be caused by the action of the oxygen of the air, and, if so, would be in- 

 duced more speedily by some vigorous oxidizing agent, Dumoulin tried the 

 effect of dilute nitric acid on glue, and shortly found that by its use the 

 product he desired was easily obtained. His method of preparation was as fol- 

 lows : The best Cologne glue is dissolved, at a gentle heat, in an equal weight 

 of water contained in an enamelled or glazed vessel, and when the solution is 

 complete, nitric acid of thirty-six degrees Beaume is added in proportions, 

 and at intervals, to the amount of one-fifth of the weight of the glue em- 

 ployed. Nitrous vapors are abundantly. given off, and a glue is obtained 

 that is perfectly fluid, and may be kept in open vessels for years without 

 alteration. Already, in 1832, this preparation was sold in Paris as inalter- 

 able liquid glue (colle I i guide et inalterable). A better liquid glue than that 

 just described is made with acetic acid. One pound of good glue is dis- 

 solved, Avith heat, in a mixture composed of one pound of strong vinegar, 

 one-quarter of a pound of alcohol, and a very little alum. According to 

 Cavallius, however, alum destroys the tenacity of glue, and should be 

 avoided. In order to make the glue white in color, a quantity of sulphate 

 of lead is added to the solution. The liquid glues now so extensively sold 

 in this country are made with acetic acid, and those we have tested are 

 very excellent preparations. A glue that is liquid at low temperature is not 

 so adhesive as one which requires gentle warming 'to make it flow. Solu- 

 tions of chloride of barium, bichromate of potash, and some other salts, as 

 well as all the various mineral and vegetable acids, also have the property of 

 holding glue in permanent solution. 



THE ART OF DENTISTRY. 



Few persons realize the rapid growth of dentistry as a profession. Forty 

 years ago doctors officiated as tooth-pullers, and if decay seized upon a 

 molar it accomplished its work unimpeded. It is an actual fact that in 1820 

 there were hardly more than thirty practising dentists in this country. Ten 

 years after that, the invention of artificial teeth had given such an impetus 

 to the profession that the thirty had increased to 200. In 1842 it was esti- 

 mated that there were 1,400; in 1818, 2,000. In 1850, the census reported 

 2,923 practising dentists ; and at the present time there must be at least 5,000. 



