CHEMICAL SCIENCE. 227 



composition of the incrustations I have found very similar ; with few 

 exceptions, crystalline in structure, and always composed chiefly of 

 sulphate of lime, the other ingredients rarely amounting- to 5 per cent, 

 of the whole." Fluorine was detected in incrustations from Atlantic 

 steamers, and also from those navigating the British seas. " In many 

 instances, oxide of iron, the black magnetic oxide, was found to form 

 a part of the incrusting deposit, collecting in one or more thin layers, 

 and in some, especially of steamers navigating the narrower and least 

 clear parts of the British Channel, the depositions presented a brown- 

 ish discoloration produced by the admixture of a small quantity of 

 muddy sediment. Incrustations so discolored are said to be most diffi- 

 cult to detach." The structure in most cases was not unlike the 

 fibrous variety of gypsum. The specimens examined varied from a 

 line and less to half an inch in thickness. In but few instances has 

 information been obtained as to the time during which the incrustations 

 were forming. In the boiler of the Europa, after a voyage across the 

 Atlantic of eight and a half days, the thickness of the incrustation 

 was one fiftieth of an inch, and was about the same on the outward 

 voyage. The precaution of "blowing off' was used every three 

 hours, and the " brine-pumps " kept constantly working. " In other 

 seas, especially contiguous to shores, and more especially to shores 

 formed by volcanic eruptions, it is probable, cceteris paribus, that the 

 rate of deposit is more rapid, and some observations are in favor of this 

 conclusion." 



Various methods of preventing or mitigating this evil have been, 

 proposed, but the most effectual one is that of " blowing off," that is, 

 " the discharging by an inferior stop-cock of a certain quantity of the 

 concentrated water of the boiler by pressure of steam, after the ad- 

 mission above of an equivalent quantity of sea-water of ordinary den- 

 sity. But this can be viewed only as a palliation." The use of 

 distilled or rain water is, however, an almost certain preventive. As 

 it is impossible to obtain this always, at present, the great object must 

 be to economize the escape of water in the form of steam, to use fresh 

 water when available, and especially to avoid sea- water near coasts, 

 where sulphate of lime is most abundant. 



Examinations have also been made in two cases of incrustations 

 from the boilers of locomotives, and in one case, from a running en- 

 gine. The latter specimen "was fibrous, about half an inch thick, 

 consisting chiefly of sulphate of lime with a little silica and peroxide 

 of iron and a trace of fluorine. The former specimens were from one 

 tenth of an inch to an inch thick. They were gray, laminated, and 

 with much the appearance of volcanic tufa ; they consisted principally 

 of carbonate and sulphate of lime, with a little magnesia, protoxide of 

 iron, silica, and carbonaceous matter, the last two ingredients being 

 probably derived chiefly from the smoke of the engine and the dust 

 in the air. From the engineer's report it would appear that the in- 

 crustation, which was one tenth of an inch thick, had formed in about 

 a week, during which time the locomotive had run about 436 miles, 

 and consumed 10.900 gallons of water." 



In the course of a lecture on the " philosophy of a kettle," Dr. Far- 



