MECHANICS AND USEFUL ARTS. 39 



than is consumed in the transformation of water into steam, and the conver- 

 sion of fixed into volatile products. But it is by no means a matter of indif- 

 ference whether the oxygen requisite for complete combustion is drawn 

 from the atmosphere or is derived from the decomposition of water by car- 

 hon and its oxide. In the former case, not only is there a great loss of heat, 

 carried away by the inefficient nitrogen of the air, but the diluted oxygen 

 can never produce so intense a heat with the carbon as is the result of the 

 reaction of the nascent oxygen with that element. Although Mr. Thomp- 

 son was no chemist, he did not fail, with his natural acumen, to perceive this 

 advantage; and in his earliest patent he remarks: "After ample experi- 

 ments, I have discovered that any results that can be produced by the use of 

 dry fuel are inferior to those obtained from my process in proportion to 

 the quantity used, and that results like mine can only be obtained by the use 

 of wet fuel . . . fed into an intensely heated chamber. Under such cir- 

 cumstances, the water in the fuel, in presence of the carbonaceous sub- 

 stances in the furnace, will be decomposed, giving its oxygen to the carbo- 

 naceous matter, dispensing with a draft and its cooling and wasteful influence, 

 and rendering the combustion so perfect that no smoke is visible." 



Although this mode of combustion of wet fuel is now in use on many 

 sugar plantations in Louisiana, and in some tanneries of Pennsylvania and 

 New York, no notice of it has, so far as I am aware, appeared in the scien- 

 tific journals. I am not without personal experience of its operation on a 

 large scale, having, in 18o7, enjoyed the opportunity of studying carefully 

 the management of one of Thompson's furnaces, in three compartments, 

 built for the combustion of wet peat. That fuel contained over seventy -five 

 per cent, of its whole weight of water, and was too wet for the best results. 

 But with the use of one fourth part of dry wood, even this extremely wet 

 and otherwise valueless fuel was rendered efficient, three cords of one 

 hundred and twenty-eight cubic feet of wet peat, and one cord of dry 

 wood, doing the work of four cords of dry wood in driving a steam boiler. 



FRICTIOXAL GEARING. 



Frictional gearing is coming into successful use in Great Britain for all 

 purposes, from small machinery up to the driving of the screws of steam- 

 ships. Instead of one wheel driving another by the intersection or "mash- 

 ing" of the " cogs" or teeth on their rims, the adjacent surfaces or faces of 

 the wheels are grooved lengthwise, or in the direction of their motion, like 

 the rolls of a rolling-mill. These grooves are V-shaped, and the friction of 

 the Vs of one wheel against the sides of the V's of the other wheel is so great 

 that the one drives the other, as in the case of cogs. The friction of the 

 journals of the shafts is somewhat greater than in the case of toothed gear- 

 ing, but in other respects the frictional wheels seem to work most smoothly. 

 The " back lash," or rattle of teeth, especially when worn, is prevented. 

 The chief economy is in first cost. The cutting of the teeth of gearing 

 involves the application of abstruse mathematical principles; each side of 

 each tooth is shaped to an epicycloidal curve, varying with the diameters of 

 the wheels. The machines and processes required are expensive and numer- 

 ous, especially in cases of beveled gearing. But the preparation of frictional 

 gearing is the most simple and straightforward work of the turning-lathe. 



