TRANSACTIONS OF THE SECTIONS. 231 



Pol)^;. J. ccxii., by Dr. Ferd. Fischer, confirmatory of these remarks, and showing 

 the influence of elevated temperature and pressiu-e on the decomposition of various 

 salts in water. 



Corrosion. — Causes of corrosion of exterior of boilers are briefly glanced at, 

 including damp settling, accumidation of damp ashes and of soot, accompanied by 

 careless tiring, which causes sulphur, acids, and other corrosives to combine with 

 the soot. 



\s'\ih regard to corrosion of the interior of boilers, investigations on various cor- 

 roding forces are first quoted. Prof. Grace Calvert's experiments on the action of 

 sea-water and of various gases on metals are alluded to, to prove that sea-water 

 exerts such an action upon steel and iron, that carbonic acid, in presence of water, 

 acts energetically, and that distilled water, free from gases, has no action. 



The application of these researches by W. Kent (of the Stevens U.S. Institute 

 of Technology) to the examination of the corrosion of iron railway-bridges in the 

 United States is then referred to ; and the investigations of A. Wagner (from 

 Dingl. Polyt. J. ccxviii.), on the influence of various solutions on the rusting of iron, 

 are quoted. This author corroborates Calvert's report of the action of carbonic 

 dioxide, and notes the fact that the presence of chlorides of magnesium, ammonium, 

 sodium, potassium, barium, and calcium in water largely increases the production 

 of rust, the action of chloride of magnesium alone being increased by heat. 



These facts correspond with that observed by J. Gamgee, that lime solutions 

 used as media of congelation in ice-making corrode the pipes or channels which 

 convey them. 



Stingl's valuable contribution to this subject, viz., his paper on the effects of 

 condensed water containing grease on boilers fed with it (Dingier, Polyt. J. ccxv.), 

 is quoted at some length. 



This author proves that gi-ease, with a small quantity of salts of lime and mag- 

 nesia, at a temperatiure not exceeding 60° to 70° Cent., forms lime-soap, which, 

 under the influence of a higher temperature, partially decomposes iuto free fat 

 acid and a basic lime-soap, which adheres to the boiler-surfaces, the free acid, 

 which is usually oxalic acid, attacking and dissolving the iron. In the crust the 

 fat is recognized by the addition of hydrochloric acid, the separated organic mass 

 being afterwards shaken with ether. 



Even with lime and magnesia salts present in very insignificant proportion, the 

 presence of grease is injurious, as, with saponification, under considerable pressure, 

 a small quantity of lime suffices to occasion the splitting up of a neutral fat into 

 free fat acid and glycerine. With low pressure the same action proceeds more 

 gradually. 



Various cases of corrosion from greasy water are noticed by this author, and in 

 particular that of a steam-boiler of Cornish design, into which the condensed steam 

 from two engines (of 300 and 100 horse-power) was fed. This boiler was con- 

 structed of steel ; and after only three weeks firing was leaking in the fire-tubes. 

 A deposit was found adhering to the upper part of the tubes, of which the analysis 

 is given. The water in the boiler had a milky appearance, which was at once re- 

 moved by ether. Ether is recommended as a good qualitative test for the presence 

 of grease in water. 



The analysis of the condensed feed-water is given, and the various operations in 

 testing the deposit from it also recorded. 



Means were adopted to purify this water by precipitation of the calcium carbo- 

 nate and part of the magnesium carbonate along with the grease, which was can-ied 

 down with the precipitate, and by subsequent filtering ; and the analysis of the 

 purified water is given. The boiler afterwards worked for three months with this 

 water without any bad results, a pure deposit, consisting principally of magnesium 

 hydrate and calcium cai-bonate and sulphate, being found to a small extent on the 

 surfaces of the boiler. 



Finally a letter addressed by the author to ' Engineeiing ' (Oct. 1874) is 

 referred to, in order to call attention to the difference between pure natm-al waters 

 and genuine distilled water, i. c. distilled water free from air. The difference con- 

 sists in the presence of gases in all natural waters. The distilled water from sur- 



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