ACTION OF WATER ON IRON. 285 



I have entered rather at length upon the mode of taking these 

 specific gravities, because the method in its details will be found 

 useful in other researches, as in taking the specific gravity of 

 small mineral specimens, &c., and because the precise determi- 

 nation of the maximum and minimum specific gravity of cast and 

 wroiight iron is of importance to the iron founder and engineer, 

 as giving the data upon which the weight of castings are esti- 

 mated, and which, as usually stated by authors, are an unsafe 

 guide, inasmuch as the specific gravity of cast iron varies with 

 its composition, the way in which it is cast, the rate of its cool- 

 ing, and the depth of the mould, to an extent not generally 

 known. 



72. I was favoured by my friend Mr. William Fairbairn, of 

 Manchester, with a few specimens of the same hot and cold- 

 blast irons, on which he and Mr. E. Hodgkinson experimented 

 as to their cohesion, so that not only the physical properties of 

 these will be known from the experiments of these, gentlemen, 

 but their durability from the present. 



73. Some specimens of Irish iron from the Arigna works, 

 county Leitrim, are also included, and some experiments, made 

 by Messrs. Bramah, of London, upon its strength are given, on 

 the authority of the agent of the works, as an appendix to the 

 tables, by which it will appear, that in point of cohesion this 

 iron ranks with almost any in Britain, while its fluidity in 

 easting recommends it as equal to the best Scotch iron. It is 

 sold on the terms of the latter in the market. — This iron being 

 scarcely known out of Ireland, these experiments and remarks 

 will not be deemed irrelevant. 



74. Four other similar boxes have been prepared, which all 

 contain a selection of specimens coordinating with those in 

 No. 1. The second box, No. 2, is sunk and moored in the 

 foul and putrid sea water at the mouth of the Kingstown town 

 sewer, where it debouches into the sea. 



The water here is 2 feet deep at ebb, and from 8 to 12 feet at 

 flood tide, and a constant succession of bubbles of sulphuretted 

 hydrogen and marsh gas pass thro\igh it from the deep deposit 

 of mud which forms the bottom. 



Precautions have been taken to prevent the box of specimens 

 sinking in the mud. The temperature of the water is 58° Fahr.; 

 it contains as much saline matter, except during heavy rains, as 

 the clear water of the harbour — its specific gravity, when filtered, 

 being the same. 



The results of this experiment will determine the relative 

 actions of clear and foul sea water, when examined in the same 

 way and at the same periods as No. 1. 



