300 EIGHTH REPORT 1838. 



practical man than any experiments made on a small scale, it 

 so happens that I am enabled to present an actual instance from 

 the Dublin Docks of cast iron deeply acted on and corroded in 

 a period of eighteen years, though in close contact with brass. 

 This is a portion of a sluice, situated between high and low 

 water, made eighteen years since by the firm to which I belong, 

 and lately obliged to be removed and replaced with a new one, . 

 in company with several others, from the deep corrosion and 

 softening it had undergone. 



The brass was here a facing riveted to the cast-iron sluice all 

 round, to make it water tight. The composition of this brass 

 differs from Mr. Hartley's only in containing some more zinc, 

 of which his contains but a very small quantity, which by ana- 

 logy and according to Mr. Hartley's own view is ail in its fa- 

 vour. Here, then, is an experiment of eighteen years' duration, 

 which results in showing that brass has had no protective power 

 in the tidal water of the River Liffey. 



117. It appeared worth while to make a quantitative analysis 

 of Mr. Hartley's brass and of this from the Dublin Docks, both 

 for the purpose of comparison, and to see if they were atomic 

 compounds or mere accidental mixtures with approximations to 

 atomic constitution, as is generally the case in brass used for 

 engineering purposes, whicli is produced by remelting. I ac- 

 cordingly analyzed a fragment of tlie first specimen of Mr. Hart- 

 ley's brass, sent us direct fi-om Liverpool, and also of the Dub- 

 lin Dock brass, and lastly, that given us by Dr. Kane. The 

 method adopted with all was the following, which differs in 

 some respects from the modes usually recommended for the 

 analysis of brass, and which are incapable of giving results ap- 

 proaching correctness. 



1st. A given weight of brass was dissolved with heat, con- 

 tinually agitating in strong nitric acid, which was boiled nearly 

 to dryness, diluted with water, and the stannic acid separated, 

 washed, ignited, and weighed. 



2nd. Tiie solution and washings evaporated nearly to dryness, 

 sulphuric acid added, evaporation continued to dryness, water 

 added, and sulphate lead, separated, ignited, and weighed. 



3rd. The solution being acid, treated with sulphuretted hy- 

 drogen, and precipitate washed in water impregnated with the 

 same; the CuS — redissolved in aqua rcgia, with heat, again 

 precipitated hot with caustic potass washed with hot water, ig- 

 nited, burning filter and weighed. 



4th. The solution and W'ashings concentrated, and pure am- 

 monia added in excess, and the Fe^Og separated and weighed. 



5th, Bicarbonate potass added to the filtered solution, boiled 



I 



