280 Mr Russell on a Marine Salinoineter for indicating the 



The remedy for these evils was veiy early invented. But 

 I have not been able to discover the inventor of the cleansing 

 process commonly called " blowing down," or " blowing off." 

 It is almost universal, and is performed in the following way : 

 —There is forced into the boiler, at each stroke, rather more 

 water than is required for the supply of steam, so that the 

 boiler becomes too full. Openings are then suddenly made at 

 the bottom of the boiler, and the brine at the bottom being 

 violently ejected, carries with it any solid substances that may 

 have accumulated near the bottom — the boiler is thus cleansed ; 

 and before the water has got too low, the openings are again 

 closed, and the boiler continues to be fed as formerly. 



Another remedy, pretty generally adopted, is the brine- 

 pump, by which, for every portion of water supplied to the 

 boiler, about one-fourth part of that quantity of brine is with- 

 drawn from it. This process does not so thoroughly carry off 

 all the impurities as the former ; but it is attended with a 

 saving of fuel by a contrivance for giving to the feed-water 

 entering the boiler a portion of the heat of the discharged 

 brine. The recent introduction of this process is due to 

 Messrs Maudslay and Field of London. 



In whatever way the saturation of the water with solid mat- 

 ter may be remedied, it is essential to the accomplishment of 

 this object, that some simple apparatus should be contrived 

 for the purpose of shewing when the cleansing process is re- 

 quired, and whether it is successfully applied. If this be not 

 obtained, the usual consequence of acting on wrong data are 

 sure to follow. 



A contrivance was patented, which was thought promising, 

 but was found liable to be mechanically out of order when 

 most wanted ; — a ball of gi-eater specific gravity than salt 

 water was connected with an external index, by which there 

 was indicated on the outside the fact of the brine becoming 

 sufficiently saturated to float this ball. 



Another was to place in the glass gauge of the boiler a glass 

 hydrometer bead, which would float when the brine became 

 saturated to a given point, and fall to the bottom in the ordi- 

 nary state of the boiler. But this fails entirely of accuracy, 

 although very elegant, for the brine of which we wish to indi- 



