PRESERVATION OF FRUITS, ETC. 



191 



tooth to its end; the wire is kept stretch- 

 ed during the operation: the curve thus 

 formed is an involute. The point which 

 traced this, is then to he made fast at 

 the place of beginnins:, and the other 

 side of the tooth traced in like manner 

 with the point of the other needle; the 

 two are then made fast at the base of the 

 cog or tooth, and a mark made with pen 

 and ink on the wheel or pattern, at the 

 base of each tooth, opposite to the re- 

 spective marks or divisions on the wire. 

 The wire is then moved round equal to 

 the thickness of a tooth and the space 

 between two; and another tooth laid off, 

 or marked from base to end, as the one 

 before described, and in like manner all 

 the teeth which are of tliat character. 

 These are convex involute spin' teeth. 



2. When teeth are formed upon a 

 concave surface, they are to be concave 

 involutes, formed from a circle at the 

 ends of the teeth. 



3. In a straight rack the acting faces 

 of the teeth are parallel with each other, 

 and at right angles to its motion. 



4. Face wheels have tiie faces of 

 teeth parallel with the axis of the wheel. 



Bevil wheels, wilh teeth on the con- 

 vex surface, are a modification of spur- 

 wheels already described, and are laid off 

 on the same principle, one being on the 

 surface of a cylinder, and the other on 

 the surface of the frustum of a cone: the 

 teeth may be laid off upon one end, or 

 both, whichever may be most convenient; 

 care should be observed to have the 

 acting sides of the teeth in the same planes 

 as the axis of the wheel. When they 

 are laid off from one side, the large end 

 of the fr-jstum of the cone is to be 

 preferred, and the base, sides, and 

 ends of the teeth, be formed of straight 

 lines pointing toward the apex of the 

 cone. These are convex involute bevil 

 teeth ; and those upon the interior sur- 

 face of the frustum of a cone also, are 

 composed of straight lines, pointing to- 

 ward the apex of the cone, and are con- 

 cave involute bevil teeth. 



Those upon the exterior and interior 

 surface of a cylinder, have the acting 

 faces composed of straight lines parallel 

 with the axis of the wheel. Face wheels 

 have the teeth made convex, in the line 



of the wheel's motion, in proportion to 

 the diameter of the wheel into which it 

 is to work, or be engaged, and the teeth 

 on the interior or concave surface of a 

 rack, are made similar to those on the 

 interior surface of a cylinder of the same 

 curve; and those upon the exterior (or 

 convex) surface of a circular rack, are to 

 be made similar to those on the exterior 

 convex wheel of the same curve. A 

 sm.all flexible thread, or a rigid straight 

 edge, with a point or scriber attached, 

 may also be used to trace the involute 

 curves upon the edges of the teeth ; but 

 as the thread is liable to stretch, and 

 there is some difficulty in preventing 

 the straight edge from sliding upon the 

 circumference of the wheel, the wire is 

 preferable. 



It appears to the writer of this, that 

 the teeth of wheels and racks, made upon 

 the principles here described, will fulfil 

 the aforesaid conditions, better than 

 where the acting sides or faces are com- 

 posed of epicycloidal, cycloidal, or con- 

 centric circular curves, or any part of 

 either; and that the involute can be con- 

 structed as rigorously correct as either; 

 and with as little labor. E. 0. R. 



FLAME OF HYDROGEN RENDERED 

 LUMINOUS, 



Dr. Hare, of Philadelphia, has render- 

 ed the flame of hydrogen luminous, like 

 that of oil, by adding a small quantity of 

 oil of turpentine to the usual mixture for 

 generating that gas. The light seems 

 greater than that of carburetted hydrogen. 

 He found also that the addition of l-17th 

 of oil of turpentine to alcohol gives this 

 fluid the property of burning with a 

 highly luniinous flame, and there is a 

 certain point in the proportions when the 

 mixture burns without smoke like a gas 

 light. — Reg. of virts and Sciences. 



PRESERVATION OF FRUITS BY CARBONIC 

 ACID GAS. 



Cherries, grapes, pears, apples, and 

 chestnuts (and perhaps all other fruits,) 

 l^laced in glass vessels filled with this 

 gas, obtained from carbonate of lime by 

 sulphuric acid, are said to be preserved 

 without undergoing any change for a 

 long period. Cherries at the end of six 



