6 APPENDIX. 



with equal success and satisfaction ; and from three years' experience of its advantages, when 

 applied to the cleaned surfaces of the defective parts, I suggest its use under similar circum- 

 stances in iron boilers ; although inconveniences here alluded to are less frequent and more 

 easily checked in these boilers, by the usual method of chincing, &,c. It must be understood 

 that I here confine myself entirely to cases where mechanical skill is found to be ineffectual ; 

 the cement need be resorted to only when every other means has failed. 



I also conceive that copper boilers experience more deterioration than iron from these 

 deposits ; the bottom flue plates of a copper boiler, upwards of f of an inch in thickness, 

 (where water was present, as before described,) being totally decayed in twelve months ; 

 the side of the plate exposed to the action of the salt water alone being unimpaired ; 

 a fact which I never witnessed in an iron boiler under similar circumstances. Hence the 

 rapid decay of boilers if these deposits are allowed to remain in the flues an unwarrant- 

 able space of time. The only mode, of course, to obviate this, is to sweep the flues as often 

 as convenient ; and the boilers, it should be provided, are to be kept perfectly dry when 

 not employed. 



12. To keep those parts of the boilers clean which are exposed to the influence of the 

 boiling salt water, it appears to be absolutely necessary to hold the salts in solution, since 

 deposits are separated from the water some considerable time before salt is formed, and at 

 a much lower temperature ; 220 having been esteemed a limit (under the pressure of the 

 atmosphere) at which a boiler begins to incrust, while my experiments have shown that 

 215 should be the maximum. Professor Faraday's experiments on sea water appear to con- 

 firm these observations : 1000 parts of sea water being evaporated, 825 parts of steam could 

 be drawn off before any deposition commenced ; but then the sulphate of lime was deposited ; 

 and proceeding till 110 parts remained, the common salt began to crystallize and deposit 

 till 35 parts remained only ; when the muriatic acid, from the decomposition of the muriate 

 of magnesia, began to separate. About f ths of the water may be raised in steam before the 

 salt is deposited. 



13. To obtain the required condition, I recommend that the practice of blowing-out should 

 be periodically and promptly attended to in the Channel as well as at sea, so as to effectually 

 expel the earthy matters while agitated, and prevent induration. I also suggest the expediency 

 of engineers strictly examining their boilers prior to a long voyage, in order to ascertain that 

 their blow-out cocks and pipes are in perfect order. A due circulation of the water in the 

 respective boilers should likewise be attended to, that the blowing-out may equally influence 

 the whole ; and blow-out cocks especially should be so arranged and adjusted, that their 

 use may be quite practicable on all occasions at sea ; as the due performance of the 

 boilers, and consequently the certainty of a passage, materially depends on attention to 

 these particulars. 



14. The construction and arrangement of the blow-off cocks and pipes of most vessels in 

 her Majesty's service were formerly very defective : in some instances, four or five men were 

 summoned to attend when the boilers were blown off, in order to shut the cocks, which 

 were often jammed by expansion ; in other instances, the boilers were blown off through 

 the hand pump, to obviate the risk of the cocks jamming. The boilers, in consequence, were 

 insufficiently attended to ; the construction not admitting these duties to be performed at all 



