166 History of Mechanical Inventions, and 



of water into vapour, of which the capacity is to that of water as ,8474: 1, 

 consequently the quantity of heat which will raise a given weight of water 

 960°, will raise the same weight of steam 1 133°— and 824° + g 824°= 

 1133° and as an increase of 1° of temperature will produce on the elastic 

 fluids an expansion of j J^ of the initial volume ; 824° will augment the 

 volume 2965,248, or increase 1728 inches to 4693,248. 



Hence it appears that a given quantity of heat, when applied to water 

 in the usual manner, produces an effect represented by 3456, 



And that when one-half of the same quantity is applied to water, 



and the other half to the steam generated by the first portion, 



the effect is represented by, 4693,248 



giving to the second mode of application an advantage equal to about ,358 

 of the total efficiency of the heat, when wholly applied through the aqueous 

 medium. On examination it will be observed that this result is lower 

 than that obtained by Mr Gilbert. 



It appears that were the amount of inertia to be overcome at the com- 

 mencement of the stroke inconsiderable, the expansive mode of working 

 could be carried to but very small extent ; it being the necessity of a much 

 greater force than that required to keep the load in motion, when once 

 moving, that permits the steam entering the cylinder and acting on the 

 piston, to acquire an elasticity greater than sufficient to continue the mo- 

 tion. Consequently, that, if the force of the steam in the boiler be not 

 considerably greater than the load on the piston, motion cannot obtain. In 

 fact, that the steam engine must of necessity have always worked expan- 

 sively, although probably in the commencement of Mr Watt's career, in a 

 less degree than it afterwards obtained. The advantage accruing there- 

 from belongs, therefore, in some degree to engines worked by steam of low 

 elasticity. I believe the additional quantity of steam which is required, in 

 order to supply the diminution of elasticity attendant on the increased ca- 

 pacity, by enlargement of volume, has never yet been taken into account. 



This will be greater as the elastic force of the steam employed increases, 

 and is certainly an additional argument to the many already adduced, against 

 the use of high pressure steam. The amount of this drawback may be 

 calculated without difficulty. But before we can arrive at a correct esti- 

 mate of the quantity of steam required for an engine of given dimensions ; 

 it seems that the amount of inertia should be accurately ascertained ; and 

 as the dimensions of the shaft work, and the amount of friction vary so 

 very much, it appears that an extensive series of experiments on this point 

 are much to be desired. It has long been acknowledged by the most stre- 

 nuous advocates of the economy of highly elastic steam, that the effect ob- 

 tained has been considerably less than theory led them to expect. 



6. On the use of Steatite or Soapstone for diminishing- Friction in Machi- 

 nery. By Mr E. Bailey, Boston. 

 This mineral has been long in use at the extensive manufactories at Lo- 

 well, in North America. For this purpose it is thoroughly pulverised, and 

 then mixed with oil, tallow, or tar, whichever may be the best adapted to 



