230 REPORT — 1876. 



to seek in a combination of chemistry and mechanical science for the needed eluci- 

 dation of its problems. 



The course of investigation has been marked by the suggestion of various em- 

 pirical remedies, which are pointed out, but which have failed to reach any good 

 result, the actions to be counteracted not being understood. 



Incrustation and corrosion are not one action, but dissimilar ones, although they 

 are often found united in boilers, and therefore both must be noticed. 



Incrustation is first considered, Dr. J. G. Rogers, of Madison, U. S., being quoted 

 (from ' Chem. News,' vol. xxvi.) for the non-conductibility of crusts and the pro- 

 portionate increase of temperature which their presence in boilers renders necessary. 



Boilers subject to incrustation are divided into two classes : — 



1. Land boilers using natural fresh waters ; and 



2. Marine boilers using sea-water. 



1. The average quality of natural fresh waters is illustrated by analysis of Eiver- 

 Clyde water, as formerly supplied to Glasgow ; and an analysis also by Dr. Wal- 

 lace of crust deposited from that water is given. The case is then quoted of the 

 boilers at a mill in Barrowfield still using that water, but in which the formation 

 of crust is prevented by the use of a quantity of soda-ash. 



The action of soda-ash under these circumstances is described; it causes the' 

 decomposition of the sulphate of lime and rapid deposition of the neutral carbonate 

 as powder. Where bicarbonate of lime is present, it is also precipitated as neutral 

 carbonate in a powdery form, one equivalent of carbonic acid being liberated. 

 Neutral carbonate being thus formed rapidly, has not power to adhere to boiler 

 surfaces ; while, if deposited slowly by heat from the bicarbonate, it is crystalline 

 and does adhere. 



M. Bidard of Rouen, author of papers on this subject in ' Annales Industrielles,' 

 has made numerous examinations of boiler-crusts, which show, according to him, 

 that organic matter has power to agglomerate carbonate of lime and form crust 

 by a process of " baking." His opinion is quoted from one of his letters to the 

 author. 



Fresenius, quoted in a paper by Dr. Wallace in ' Proc. of the Phil. Soc. of Glas- 

 gow,' vol. iv., ascribes this agglomerating power to sulphate of lime. Bidard's 

 explanation applies where carlDonate and not sulphate of lime predominates, because 

 sulphate is able to form crusts where no organic matter is present, as in some 

 crusts from marine boilers. The use of too much soda-ash is inj urious, and pre- 

 cautions are given, with a little further illustration of its action in boilers. 



It is proposed to apply it in the feed-tanks or cisterns generally attached to 

 boilers, allowing the lime to be deposited there to save constant blowing off. 



Various other preventives of incrustation are noticed, including De Hiien's 

 method of using barium chloride and milk of lime, founded upon the investiga- 

 tions of J. Y. Buchanan (Roy. Soc. Proc. vol. xxii.) , and some details of comparative 

 cost in working with this process are given from Dingler's Polyt. J. ccxvii. _ 



As the most complete preventive of incrustation, which is otherwise scientifically 

 desirable, the author advocates the use of surface condensers in connexion with 

 land boilers. 



2. Although modern systems of marine engine practice have removed incrusta- 

 tions from marine boilers by the introduction of surface condensation, there is still 

 some necessity to consider incrustation as applying to them, because of a tendency 

 to return to the ancient regime in consequence of difficulties with corrosion. The 

 evil effects of incrustation are felt more heavily in marine practice from its con- 

 ditions of using sea-water, which contains a large amount of solids, and of limited 

 space for carrying fuel and chemical reagents and for repair of boilers. 



The inappHcability of the chemical method is pointed out, reference being made 

 to experiments of Mr. Jas. R. Napier, F.R.S., published in Proc. Phil. Soc. Glasg. 

 vol. iv. 



Working with fresh water is the only sensible and efficacious method ; but when 

 this has been used it has brought with it the evils of corrosion. 



Analyses of sea-water from the Black Sea, and of six samples of marine-boiler 

 crusts found at various pressures, are added, with remarks on some of these by 

 Dr. Wallace (from Proc. Phil. Soc. Glasg.), and extracts from a paper in Dingler's 



I 



