385 



, I have several times been asked whether some acid could 

 not be added to the water which should hold the lime in 

 solution. 



No doubt it could, but alas ! for this class of projectors, 

 the excess of acid would act ferociously, at the boiling 

 temperature, upon the metals themselves. Dr. Clark, of 

 Aberdeen, has a patent for the use of lime water in such 

 proportions as shall exactly saturate the excess of carbonic 

 acid, and precipitate both the carbonate of lime originally 

 present, and that formed from the lime added. The pro- 

 cess is ingenious, and does credit to Dr. Clark's sagacity, 

 but I fear it would not apply to railway waters. It would 

 leave the sulphate of lime ; its efficacy in any case depends 

 on the exact adjustment of the lime added to the free 

 carbonic acid in the water ; as this varies, so must the lime 

 water to be added ; and I fear that engineers would recoil 

 from the apparatus of settling tanks, or of filters, needful 

 for clearing the water from the carbonate of lime, after it 

 had been reduced to the insoluble form. We are therefore 

 thrown back on the selection of the best waters which the 

 neighbourhood of a station may afford ; on chemical analy- 

 sis to assist in that selection ; and in those situations where 

 none can be obtained but what is of poor quality, drawing 

 off the residual portion, or what is called, I believe, blowing 

 off frequently ; and what is of equal consequence, as early 

 as possible after a journey, or course of journeys, so as 

 not to allow time for adhesion in a firm crust to take place 

 to the utmost. 



As my object in the present instance has been to point 

 out to engineers how they may best apply the resources 

 of chemistry, in their own hands, or those of others, 

 to the selection of water, 1 may add one or two further 

 remarks. Waters collected in districts where the strata 

 are siliceous are generally most pure the nearer they 



E E 



