EXPLANATION OF THE PLATES. 381 



M, Is the air pump, through which the bucket M' discharges the water resulting 

 from the condensation of the steam from the cylinder, in its passage through the 

 pipes 1515, together with the air and uncondensed vapour, into the hot well Z, through 

 its valve 1 7, whence it is carried forward by the feed pipes into the boiler A. 



Still, in order to meet unavoidable losses of water from the boilers by the waste of 

 steam., &c., a distilling vessel A', of cylindrical figure, is introduced within the boiler, 

 which uniformly maintains the requisite height of water therein, in the following- 

 manner : 



A pipe 1 8, connecting the upper surface of the still A' with the upper or steam 

 chamber 1 3, of the condenser, is furnished with a stop cock 1 9, which when open per- 

 mits the vapour generated in the still to pass over into the condenser, whence it is 

 returned by the feed pipes, in addition to the water resulting from the steam of ex- 

 haustion, into the boilers, and is regulated in quantity by the amount of opening of the 

 stop cock 19. 



The connection with the condenser produces a nearly corresponding vacuum in 

 the still, whence evaporation takes place at a lower temperature and much more ra- 

 pidly than if exposed to the atmosphere at the ordinary boiling point of 212. 



As the evaporation proceeds, and the water in the still becomes lower than the 

 level marked in the drawing, the copper float 20, descends, carrying with it the rod 

 21, of the index 22, and causing the valve 23 to be lifted at the same time. The 

 valve 23, being connected with the supply pipe 24, which is joined at the other ex- 

 tremity with the waste pipe S of the condenser, affords abundance of sea water to 

 pass into the still, until again closed by the float 20 ; the index 22 exhibiting the 

 operation. 



By the frequent repetition of this process, it will be seen that the water in the 

 distilling vessel A', will become saturated with salt, and in that respect the still will 

 be assimilated, with the exception of risk from burning in case of neglect, to ordinary 

 boilers working with sea water ; it is also kept clean by the same rule, thus : 



The pipes, 18 and 24, being first shut off from the still by their respective stop 

 cocks, a communication is opened by the cock 25, with a pipe 26, which descends 

 nearly to the bottom of the still, its other end passing through the ship's side. At 

 the same time, another pipe, (not seen,) also furnished with a stop cock, allows the 

 steam from the boiler to pass into the upper part of the still, whence by its pressure 

 the brine and other impurities are completely driven out into the sea. 



These latter pipes being shut off and the former ones opened, the process of distilla- 

 tion goes on as usual. 



The piston B', acting on the cross head D, gives motion to the side rods E, which 

 are connected at the lower ends with the beams or main levers C, and these vibrat- 



