MECHANICS AND USEFUL ARTS. 59 



it is necessary to make it long enough, that when cold it may not fall 

 between the supports, but in general it seems that not sufficient play is 

 given to bars supported in this manner. Technologist, May, 18o4. 



MANUFACTURE OF IRON FOR SHIP-BUILDING. 



Robert M. Garvin, of Glasgow, has devised the following method for 

 preventing the adhesion of barnacles, and other animal matter?, or forma- 

 tions to the bottoms of iron ships when afloat. He accomplishes this end 

 by adding to, or mixing in the iron, of which the ships are to be built, a 

 small proportion of arsenic. This admixture may be effected, either when 

 the iron is in a state of fusion, or at any other suitable or convenient stage 

 in the manufacture of the metal, such as in the puddling or blooming 

 processes, when the metal is soft and plastic. 



The effect of such admixture with the iron is, that the resultant, gradual, 

 feeble solution of the poisonous matter in the water, destroys, or prevents, 

 the adhesion of all barnacles, and marine animal productions, of every 

 kind ; and thus no hold is afforded for the foreign matters which ordina- 

 rily cling to the fundamental animal formations. 



By adding the poisonous matter to the mass of metal, during the process 

 of the manufacture of such metal, the latter becomes thoroughly incorpo- 

 rated with the poisonous ingredient, so that the whole of the exposed iron 

 of which a ship is built, retains its poisonous qualities until actually worn 

 out, instead of losing such qualities by surface wear. In practice, it has 

 been found necessary to add as much of the ordinary white or yellow 

 arsenic of commerce as the iron will fairly receive, without suffering any 

 deterioration in its quality. This necessary amount of arsenic varies from 

 two to five per cent, of the iron, according as the quality of the latter 

 varies. It is preferred, to effect the admixture of the poisonous matter in 

 the puddling furnace, the addition being made just before the metal begins 

 to boil ; or, instead of this routine, the poisonous matter may be placed 

 between the metal blocks, before the latter are heated for the rolling pro- 

 cess. By pursuing this last plan, little or no loss of the arsenic ensues. 

 The patentee also finds it necessary, to sprinkle the outside plate, whilst it 

 is red hot, with a little arsenic in addition, the sprinkling to be performed 

 before completing the rolling as, for example, before the last two 

 entrances to the rollers. The poisoned plates are then well cleansed with 

 strong acid, and are scrubbed with holystone, and are immersed in a mix- 

 ture of arsenic and spelter, tin, lead or zinc. It is obvious that this sys- 

 tem of treatment is applicable to the metal employed in various details 

 concerned in naval construction. 



Iron plates treated in this way, have been tested by immersion in sea- 

 water, as well as by building them into the hulls of sea-going ships, with 

 the most favorable results. Mechanics Journal, London. 



