286 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[Septemdeb, 



ZINC-WHITE A SUBSTITUTE FOR WHITE-LEAD. 



It has been proved that zinc-white may be employed, with great advantage, 

 as a substitute for white-lead, for painting and oilier purposes forKliich that 

 substance is ordinarily employed ; as the former substance is free from the 

 disadvantages possessed by the latter, which is not only liable to turn black 

 by the action of the air, hut also produces the painters' cholic, and other 

 disorders, which are often fatal. Zinc-white is, moreover, found to be 

 unchangeable ; this fact has been proved, beyond dispute, by numerous well- 

 verified experiments ; but the principal obstacle to its employment has been 

 the difficulty of working with that material. This arises mainly from the 

 fact, that workmen, who are accustomed to a certain routine practice, are at 

 fault when a new substance is set before them ; and, after attempting to use 

 it according to the method with which they are acquainted, and not finding 

 it succeed, they immediately condemn it as useless. Although persuaded 

 of the beneficial results which would accrue from the use of zinc-white, the 

 masters will not take the trouble to look into the matter themselves, but rely 

 upon their workmen , and thus the public are persuaded that the application 

 is impracticable. Now, it is the object of the present paper to obviate this 

 difficulty, by pointing out the method of employing zinc-while with success 

 and economy. 



The first thing to be done is, to procure oil as nearly white as possible; 

 this is essential if a bright colour be required, for, as the zinc-white pos- 

 sesses less body than white-lead, coloured oil imparts a colour to it which 

 tarnishes its brightness j if, however, a yellow colour be leqiiired, there is 

 no occasion to be so particular about the whiteness of tlie oil. The most 

 •uitable oil, and which is generally sufficiently white, is the oil of the black 

 ji ippy, which may be procured from Flanders and Alsace, where it is in 

 common use; — in default of obtaining this, any other siccative oil, provided 

 it be white, will answer the purpose, although it may, perhaps, smell a 

 little stronger. 



The zinc-white is to be ground, while dry, into powder, with a mullar; it 

 riust then be scraped, with a painter's knife, into a heap, in the middle of 

 which a hollow is to be made, to receive a small quantity of oil; the whole 

 is then to be mixed with a knife, so as to hiing it to the consistency of very 

 thick mortar or paste, and rather dry than otherwise, — as this substance 

 becom es more liquid the more it is ground. This paste is then placed on a 

 separate palette, from which a small quantity is taken and put under the 

 iLullar, and triturated ; and, as the colour escapes, it is scraped up with the 

 knife, and placed in heaps on a clear space on the stone, where it is again 

 ground, — the mullar being carefully placed in the centre of the heaps : when, 

 by this means, the colour is spread over the whole surface of the stone, 

 three or four turns from one end to the other will finish the grinding ; the 

 whole must then be scraped off with a knile. This operation, which 

 appears, at first sight, tedious and troublesome, soon becomes easy of per- 

 formance, — as zinc-wbite has a fine and easily-separated grain, which, conse- 

 quently, requires but little grinding. Care must be l.iken that the colour is 

 of sufficient consistence to belaid on a flat surface without showing through ; 

 and, consequently, if it be too liquid, it will be necessary to add a sufficient 

 quantity of powder to give it the required consistency, and again grind it ; it 

 is then to be put in a clean vessel containing clear water. In this state it 

 may be mixed with any of the ordinary colours, and will be found to make 

 up with any of the colours usually combined with white-lead, producing a 

 fresher tint than when the latter substance is used. 



The natural colour of zinc-white is a milk-white, less bright than that of 

 white-lead of the best quality, which inclines to blue, but much superior to 

 that of common white-lead or ceruse; and, therefore, zinc-white may be 

 said to be the medium quality between " kremnitz" and the common white- 

 lead or ceruse generally employed for painting the interior of apartments. 

 Zinc-white may therefore be considered as an efficient substitute for white- 

 lead, without possessing any of its disadvantages. 



faints h.iving zinc-white as their base, do not dry so quickly as lead 

 colours, hut they will set more quickly than ochre : the dift'erencc in time, 

 as compaied with while-lead, is about 2 to 5 ; and, if it be ground up with 

 oil which is rather old, and not very oleaginous, it will ilrj as quickly as 

 white-lead.* When mixed with substances that do not dry easily, it will 

 only be necessary to add, as a siccative, a little white copperas (sulphate of 

 zini) ; care being taken not to use the oil piejMred with lead, usually 

 employed by painters, as it would not only turn the while yellow, but would 

 impart to it the deleterious qualities sought to be avoided by its use; if, 

 however, it is found necessary to use this oil for black or other colours 

 which will not dry, it must he used With caution. 



When large surfaces are to be painted, the brushes used must be very soft 

 and not too close, in order that the colour may be laid equally ; and, if the 

 first coat be properly laid on, the laying of the second will be unattended 

 with difficulty. 



Experience has shown, that about 2J ounces of zinc-white are sufficient to 

 cover a square yard ; while from 4 J to 5 ounces of white-lead, of second 

 quality, are required lor this purpose ; at the same time, supposing it to be 

 more expensive, this is amply compensated by the certainty that it will not 

 prove injurious, either to those employed in jiainting, or persons inhabiting 

 apartments painted with it. — Translated for A^ew Ion's London Journal. 



* By the addition ot siccative oil, colours, made wilh ziuc-wUitc, will dry as ciuickly as 

 ceruse. 



HARDENING LIMESTONES. 



On the Formation of Hi/draulic Limestones, Cements, and other Minerals, 

 in the Moist Way. By Professor Kuhlmann. 



The author had some time ago observed that all limestones contain small 

 quantities of alkalies; and be has recently found that, in hydraulic limestones 

 in particular, a very considerable amount of potash occurs. — From this ha 

 concluded that the silicate of potash must exercise an essential influence 

 upon the proiluction of cements; and he succeeded in producing artificially 

 hydraulic limestone in the muist way, by mixing lime with silica or alumina 

 dissolved in water containing some potash. When powdered chalk ii em- 

 ployed fur this purpose, the pasty mass obtained gradually hardens in the 

 air, and attains equal hardness wilh the very best hydraulic cements. If, on 

 the other hand, chalk in pieces or porous limestone is dipped into a solution 

 of silicate of potash, they acquire, after several days' exposure to the air, 

 such a degree of hardness at the surface that they scratch limestone ; they 

 admit of being polished, hut it is only with porous stones that the hardening 

 penetrates through the entire mass. This property may be usefully era- 

 ployed in the manufacture of ornaments, as, by judicious treatment, the 

 surface experiences no alteration. The silification may even be employed 

 for obtaining lithographic stones from chalk. 



Gypsum is likewise hardened in the same manner, and its decomposition 

 by alkaline silicates takes place far more rapidly and more completely. 

 Crystallised gypsum is only superficially acted upon by it; but when ground 

 and mixed with silicate of potash, it acquires a hard and shining surface. 

 If, too, concentrated solutions are employed, the decomposition is too rapid, 

 and the surface exfoliates after several days' exposure to the air. Oxide of 

 manganese and potash may be employed with the same eftect as the silicate 

 of potash. The author ascertained, by experiments, that lime has the pro- 

 perty of precipitating metallic oxides dissolved in alkalies; as, for instance, 

 oxide of copper from its solution in ammonia. He observes, on this subject, 

 that in general, every insoluble salt in contact with a saline solution, the 

 acid of which forms with the base of the insoluble salt a still more in- 

 soluble combination, produces a decomposition of the salt in solution, 

 which, however, in most cases, is incomplete. Thus white lead precipi- 

 tates a considerable qurntity of chromate of lead from a cold solution of 

 chromate of potash ; silicate of potash and chromate of lime yield some 

 silicate of lime, &c. 



The author is inclined to suppose that the crystallised silicic acid in the 

 limestone rocks, as also flints, agates, &c., owe their origin to this cause ; 

 that they have consi quently been formed by the decomposition of the silicate 

 of potash by carbonic acid. In fact, be found, in examining these minerals, 

 that, after ignition and pulverization, they communicated a decidedly alkaline 

 reaction to water. In these siliceous deposits, the two following causes 

 have been principally active : — 



1. Decomposition of the earthy carbonates by alkaline silicates, producing 

 earthy silicates, which are decomposed under certain circumstances by water 

 containing carbonic acid, and part with the eaiths. 



2. Direct deposition of silicic acid by decomposition by carbonic acid of 

 the alkaline silicate held in solution in water. 



The author finds a confirmation of his view in the circumstance that, he- 

 sides the minerals previously mentioned, manganese, dolomite, talc, asbestos, 

 emerald, corundum, sulphuret of antimony, &c., contain small quantities of 

 alkalies. — Ann. de Chim. et de Phys. 



NOTZS OF THE IffiONTH. 



Patent Decorative Glass, or Vitrified Lace-Pattern Glass. — The company 

 state that the process and effect produced are perfectly novel, and perfect 

 representations of net or muslin curtains with embroidered borders, correct 

 in every detail, and every description of lace pattern, can be undertaken. 

 The material used for the matt or ground-work is different to that usually 

 employed for the same purpose — is luore even in surface, will retain its 

 colour, and cannot in any way be affected by exposure to the atmosphere, 

 and has a semi-transparent appearance, not found in work of a similar cha- 

 racter. They consider that for internal decorations, the patent glass pos- 

 sesses a decided advantage over every other description of white ornamented 

 glass, has the same appearance from both sides, does not require the aid of a 

 light behind to show the design ; and the ornament stands out in strong 

 relief when viewed by lamp-fight. The material can be had as low as \s.id. 

 per 16 oz. 



Cleansing Buildings. — The dingy appearance of buildings in the metropolis 

 is far from creditable, hut the expense of cleaning is a great obstacle to im- 

 provement. 'I'he supposed necessity of scaffolding entails the greater part of 

 the outlay. Lately, Wren's chuich of St. Michael's, Bassishaw, has been 

 cleansed by Mr. Oldis, builder, of Basinghall-street, at a cost of 30i. only, 

 including colouring inside and out from the tower to the ground, and paint- 

 ing doors, &c. Had scaffolding been set up, the cost would have been 

 double ; whereas, the cleansing was effected by a running stage worked by a 

 derrick on the roof, with a fall and tackle. It is much to be desired that 

 Bunnett and Corpe's iron shutters were more used, so as to allow the fronts 

 of buildings to be washed down with fire-engines, as the Bank of England 

 is. Part of Mercers' Hall front has just been cleansed by washing. We 

 consider that a good business might be done in cleansing buildings on 

 reasonable terms, as an exclusive employment. 



