1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



361 



pered in July 183S,and is now in much worse condition than the Quarantine, 

 which has heen on six years longer. Tliat the waste on the Eddystone ten- 

 der is not owing to her work, is evident, from the fact, that the upper 

 part of her sheathing, which suffers the wash and friction, continues sound, 

 whilst from beneath her floor the copper peels off in blue ilakes. That this 

 is attriliutable, iu a great degree, to her occasionally grounding upon the 

 black mud, which generates sulphuretted hydrogen and other corrosive mat- 

 ters, is very probable ; the other never grounds, and does less work. Yet the 

 difference is too great to be tlius satisfactorily accounted for. The one is in 

 good condition for nine years, the other comes to patch before tlie end of 

 three : both lying the most of their time in the same harliour. On neither 

 was there any distinct indication of protective or destructive influence in the 

 nails.'' " Meanwhile, as nails must he used, and present a large metallic sur- 

 face to the salt water, as well as numerous points of contact with the copper, 

 calculated to give great effect to small electro-chemical differences, either in 

 protection or destruction, it would seem that we ought to render them slightly 

 electro-positive to rolled copper, hy the addition of zinc, which would not 

 injure their flexil)ility nor enhance their cost. The test, hy the galvanometer, 

 would be easily applied (after a little practice) in making up the metal for 

 casting them, if it is of importance to continue the present system of their 

 manufacture." 



There is another method of protection, which came out in the course of 

 these investigations ; and which is beginning to occupy pubhc attention. It 

 was before noticed, that the upper part of the copper on the Eddystone ten- 

 der, which bears the wash and friction of the waves, continues sound ; whilst 

 the bottom is fast wearing out. This exception, or rather subversion of the 

 usual conditions, is owing to a coat of fish oil, laid on when the copper was 

 new, to keep it bright ; and not extended over the parts out of sight. Such 

 a permanent effect could never have been anticipated from an oil which is 

 not drying, and strongly indicates the facility, as well as efficacy, of this mode 

 of protection. A still more striking case presented itself in the vessel which 

 suppUed the observations on the apparent influence of the nails. During our 

 examination, we observed the complete preservative effect of some coal tar, 

 which had trickled down over the copper, from the wood-work above. This 

 had crossed tlie sheets just where most subject to the wash and friction ; and 

 whilst the naked metal had been quite worn away, the coal-tarred streaks 

 remained entire, the surface of the copper, on melting off the tar, being as 

 perfect as when fresh from the roll. Hence coal tar seemed to be an efficient 

 preservative ; but then recurs the question — will it keep a clean surface, free 

 from organic adhesions and earthy incrustations ? To embrace the oppor- 

 tunity for experiments, the vessel was sheathed with copper on one side and 

 yellow metal on the other; and her fore-quarters to her mid-length varnished 

 with coal tar, laid on hot, upon the metal also heated, by fires of chips round 

 the sides. She has now heen twelve months at sea ; and, according to the 

 last account, the varnished as well as the metallic surfaces, kept quite clean. 



METHOD OF PREVENTING THE OXYDATION OF IRON. 



By M. F. L. .4.ll.\mand. 



This composition, of a metallic nature, preserves iron and steel from 

 oxydation, by entering into the pores without in any degree affecting their 

 external appearance, or leaving the least blemish, so that steel instruments 

 (including razors), tire-arms, &c., retain their poUsh, and are in some degree 

 better fit for use, after having heen subjected to the metallic application. 

 Articles either plain or chased appear superior to platina, and retain, after 

 the application, all the hieroglyphic characters, figures, letters, and other en- 

 gravings, or cuttings, which were there previously. 



COMPOSITION OF THE MATEKIAL. 



Pure Malacca Tin 120 



Silver filings 4 



Yellow tincal 12 



Purified Bismuth 12 



Purified Zinc 12 



Regulus of Antimony 4 



Nitre 11 



Salt of Persicaria 1 



Method of Purifying the Metals. — The tin ought to be melted separately 

 18 times. Each melting shoidd remain about 20 minutes exposed to the 

 action of caloric, and the impurities which arise on the surface should be 

 carefully removed ; it is thrown afterwards into a ley formed of vine twigs 

 and persicaria (herb) in equal proportions. The bismuth, the regulus of an- 

 timony, and the zinc are also melted separately, but they only require it 

 twice, and they are carefully run into an ingot mould, so that all impurities 

 may remain at the bottom of the crucible. The tincal does not require any 

 purification. 



Mixture of the different suisfances. — The tin is the first material that is 

 melted ; the silver is afterwards added to it in small quantities, and in a few 

 minutes afterwards the tincal, then the bismuth and the zinc in succession. 

 As soon as it ascertained by the flames that the alloy is effected, the two 

 kinds of salt are thrown in together, and are left to burn with vigour, and 

 the alloy is stirred with an uron rod ; after which it is earefuUy skimmed and 

 poured into a vessel, to be made use of for the metallic application. 



Method of apphjiny the mhstance. — Before the piece of iron or steel is 

 dipped in the recipient w hich contains the metallic mass already liquified, itg 

 surface must be rubbed well with a composition of sal-ammoniac and cream 

 of tartar, in the proportion of 5 per cent, of tartar to the sal-ammoniac ; the 

 iron must then be dipped in the nielted alloy, where it must remain only for 

 a few seconds, and till it is perceived to be covered with a certain quantity 

 of the metal. It is next placed in a wooden box of its own size, and in which 

 there has ))een previously put a small quantity of sal-ammoniac and cream of 

 tartar, in the proportions already indicated. It is again rubbed with a hand- 

 ful of tow, and a small quantity of the powder is put on the surface. In the 

 course of this operation the steel loses its colour, and assumes that of silver. 

 When this is done it is again plunged into the metallic mass for a few seconds, 

 and when it is taken out it is again lightly rubbed with the tow to remove 

 any superfluous particles. The article being perfectly clean and shining, it is 

 plunged into a basii; of cold water, into which there has been poured a bottle 

 of spirits of wine of forty degrees of strength, in the proportion of \ per cent. 

 .■Vfter having withdrawn it from the water, the article is rubbed carefully with 

 a linen, then it is rubbed as carefully with some fine sand, that has been 

 moistened, to remove the spots of smoke : it is at last rubbed a second time 

 with di7 sand, then with a linen, and finally with a leather. After all these 

 operations, which require great celerity in the execution, the iron will remain 

 impervious to oxygen, and by care it will preserve all its whiteness. — Inven- 

 tors' idvocate. 



APPARATUS FOR DISTILLING SEA WATER. 



We have seen iu operation, at Mr. Robinson's manufactory, Pimlico, an 

 apparatus for evaporating water in large quantities. An authentic account 

 of the apparatus has been given in the Inventor's Advocate, from which we 

 give the following details : — 



The principle on which the patent " Distillator " is constructed, is that of 

 the continuous transfer of heat through a series of vessels by evaporation. 

 Thus, steam being generated iu the boiler, is admitted into a chamlier sur- 

 rounded by water, where it is condensed, forming distilled water. From 

 that chamber the water is permitted to run off into a suitable vessel. The 

 heat transferred from the condensed steam to the water with wliich the con- 

 densing chamber was surrounded, produces renewed evaporation, and the 

 steam from that second boiler is conveyed to a second condensing chamber 

 placed in a third vessel of water. The process is repeated in that vessel, and 

 may be so continued through five or six condensing chambers. In the appa- 

 ratus we inspected at Pimlico thare are only three condensing chambers, and 

 the hot water in the last vessel is pumped back to the first boiler until it 

 becomes saturated with salt, and then it is blown off. 



As in the ordinary process of distillation only one condensing vessel is 

 used, it is evident that a positive saving of fuel must arise from the addition 

 of other vessels in which a similar process can be carried on without the 

 addition of fresh fuel. In the apparatus already constructed, it is found that 

 by the addition of two chambers to the ordinary still, an increase of distilled 

 water is obtained equal to from 130 to 140 per cent. The produce of the 

 three condensing chambers, at a minimum, are three measures from the first, 

 two from the second, and one from the third ; the two last being equal to 

 the evaporation from the boiler heated by fuel. At a maximum the quanti- 

 ties are : from the first, five measures ; from the second, four; and from the 

 third, three. This is equalto a gain of 140 per cent. 



In the report of experiments made to the Lords Commissioners of the 

 Admiralty, it was proposed to produce 20 lb. of distilled water by the com- 

 bustion of 1 lb. of coals. This was actually produced by the apparatus, under 

 a working pressure of steam in the boiler of 10 lb. to the square inch ; but, 

 as in subsequent trials, the working pressure has been reduced to 5 lb. the 

 square inch, as a measure of safety, the effect falls short of 20 lb. of water 

 for 1 lb. of coal, in a slight degree ; but in a new apparatus, this can be 

 amply compensated, by giving an increased evaporative power to the first 

 boiler of the series, and by coating the whole with felt, so as to prevent the 

 radiation of heat. In a trial of three hours duration, 59 gallons were evapo- 

 rated from the three vessels as now constructed. 



It is proposed, as a matter of convenience and safety, when tiie apparatus 

 is employed on board ship, that the fire should be placed on the U|iper deck, 

 and the distilling or condensing chambers on the lower deck, or in tlie hold. 

 By this arrangement it is expected that the same fire which is used for cook- 

 ing may be made the means of producing a constant supply of fresh water. 



By the use of this invention, the necessity of encumbering a vessel with 

 the usual cargo of water and tanks for a long voyage is entirely obviated, hy 

 merely substituting five per cent, of that cargo in coals for the distillation. 



FRESCO PAINTING. 



Mr. Haydon, with characteristic energy and enthusiasm, has made a trial 

 in fresco, on the wall of his painting room ; and the result of this first and 

 hasty attempt is decisive of two important points — the beauty of fresco 

 painting as a means of decoration, and the ease with which a knowledge of 

 the practice may be acquired. The subject is a study for the archangel Uriel, 

 the bust and arms only, of the life size ; it was painted at once on the plai- 



3 B 



