There being, however, no other known metal which possesses the same degree of flexibility and durability as lead, it was still deemed a most important desideratum to give a perfect coating of tin or other innocuous metal to lead pipe, without impairing the flexile or other valuable properties of the latter; and this we are happy to add has been supplied by a new process, very recently patented by Mr. John Warner,jun.; the specification of which describes that process to be as follows :—A bath of melted tin is prepared in a vessel of a suitable form and size, which may vary according to the size of the pipe to be tinned, (or the size and shape of any other leaden article to be tinned.) The heat of the bath is to be so regulated that the metal shall continue in a fused state, but not at a higher temperature than is necessary for that purpose, lest the lead when immersed should be melted thereby ; the heat may be ascer tained by the use of a thermometer, or a pyrometer ; likewise by testing it by such alloys of tin and lead as will melt at certain given temperatures, between the melting point of tin (or such alloy of tin as may be used as a substitute for the pure metal,) and that of lead, when placed wider the influence of a bath of melted tin. This, the reader will observe, is a very nice point, and can only be timed by great skill and attention on the part of the workmen ; for although tin melts at about and lead at sir of Fahrenheit's thermometer, yet, when they come together, an alloy is produced at the immediate points or surfaces in contact, whose fusibility is-much lower than even that of tin ; so that when, by mismanagement, the heat is raised a few degrees too high, a quantity of the lead in the form of an alloy runs off the pipe into the bath ; and if; on the contrary, the heat be suffered to fall a few degrees too low, the tin is not suffi ciently fluid, and deposits itself upon the lead in a thick and uneven coat. When the pipes are to be tinned all over, the external surfaces are sprinkled with powdered resin, and the same material is blown up the pipes so as to cover their internal surfaces with it; a mixture of oil and resin boiled together is, however, preferred to the resin alone. The said mixture is to be spread over the surfaces of the lead pipes by any convenient means, and when they have been so prepared, they are to be passed through, or immersed in the bath of melted tin, which should be covered with fat, oil, or resin, to prevent the oxidation of the fluid metal, and to aid in the tinning. But when the pipes are to be tinned on one side only, or partially, those parts which are not to be tinned are covered with a mixture of lamp-black and size, or with any other matter that will pre vent the action of the tin 'rpm the lead; and those parts that are to be tinned are to receive the powdered resin, or the mixture of oil and resin, as before mentioned. The pipes thus prepared are then to be passed through, or immersed in the bath of liquid tin, by process they will be tinned in the parts required. When the pieces of pipe to be tinned are of a small size they may be easily managed by hand ; but when they are of considerable weight or length, a rope and pulley is resorted to, to draw them through the bath of melted tin : the form of the bath is that of a segment of a cylinder having two flat sides; the chord of the segment being the top or open part of the vessel, where it forms a parallelogram of about six inches wide and two feet long. This form, it will be perceived, accommodates the bended form of the pipes, to dip in at one end of the vessel, and curving round the bottom, to come out at i the other end ; the tin thus flowing in at one extremity of the pipe, and running out at the other. This process, as we have had occasion to notice, gives a per fect coating of tin, and fills up any minute fissures or holes that there may be in the pipe, besides enabling the manufacturer to give the pipe any required thickness of coating, by drawing it any number of times through the bath. But an extremely minute quantity of tin covers the surface effectually, and by not impairing the flexibility of lead, adapts it to every purpose to which both pipes and tin pipes are used, and at the most trifling cost above that of lead.
Strength of Leaden PipeL—Some experiments urn this important subject were made by Mr. Jardine, of the Water Company m Edinburgh. The method of' proving was to close one end of a piece of pipe, and then inject water into it by means of a forcing pump attached to the other end, the force or pressure being measured by a gauge belonging to the pump. When the water from the injecting pump begins to press out the pipe, httle or no alteration is observed in it for some time. As the operation proceeds, however, the pipe gradually swells throughout its whole length, until, at last, a small protuberance is observed rising in some weak part, which increases until the substance of the pipe, becoming thinner and thinner, is at hut rent asunder. In the first experiment, the pipe was of one and a half inch bore, and the metal, which was remarkably soft and ductile, was one-fifth of an inch in thickness. This sustained a power
equivalent to that of a column of water one thousand feet high, equal to thirty atmospheres, or 420 lbs. per square inch of internal surface, without alteration; but with a pressure equal to twelve thousand feet of water it began to swell, and with fourteen thousand feet, or six hundred pounds on the square inch, it burst. When measured after the experiment it was found to have swelled until of a diameter of l e inch. The edges of the fracture were not ragged, but smooth like • knife. Ina second experiment, the pipe was two inches in diameter, and one-fifth of an inch in thickness. It sustained a pressure equal to that of a column of water eight hundred feet high, with hardly any swelling, but with one thousand feet it bunt; the fracture in this was not so fine as in the former instance, the metal being much less ductile.
Red Lead and Litharge.—We have described, at page 52, the method of refining lead for obtaining the silver which it usually contains, by which process there results an oxide of lead, called Warr. The use of this substance for making oil and oil paints dry sooner is well known; it remains to be observed in this place, that it is the material from which red lead is made. The litharge is put into pots, and exposed to the action of flame in • reverberatory furnace for forty-eight hours, during which time it is frequently stirred; hence it acquires the orange-red colour, termed minium, or red lead. There are other modes of obtaining red lead. In Germany and some other places, metallic lead is calcined on the hearth of a cupola furnace, and constantly stirred for eight hours ; then left in the furnace for sixteen hours more, stirring only at intervals. The massicot thus produced is then ground in a mill, washed, dried, and put into earthen pots, so as only to make them about a quarter full, in which they are exposed to the action of flame, enveloping them in a furnace for forty eight hours, by which time, the colour being fully developed, the pots are taken out, and their contents passed through sieves to separate any foreign or gross matter. A hundred pounds of metallic lead thus produces about a hundred and ten pounds of red lead ; the increase arising from the absorption of oxygen. The specific gravity of red lead is 8.94.
Sugar of Lead is obtained by dissolving the metal in acetic acid, concen trating the solution, and crystallizing.
Turner's Patent Yellow, now almost entirely disused, may be obtained by pouring upon litharge, one-third of its weight of touristic acid, and, after letting it stand for twenty-four hours, melting the whitened litharge, by which it becomes yellow. Gonlard's extract is made by boiling litharge in vinegar.
Chromate Yellose.—This beautiful colour, which has superseded the use of the last-mentioned pigment, is obtained by precipitating a solution of lead in acetic acid, by the addition of a solution of the chromate of potash.
Lead is rapidly dissolved by the nitric acid. Wooden sticks, impregnated with a nitric solution, made by dissolving the cuttings of lead in weak nitric acid, have been recommended by Proust, as a substitute for port-fires, in dis charging artillery. Most of the acids attack lead. The sulphuric does not unless it be concentrated and boiling. When lead is alloyed with an equal weight of tin, it ceases to be acted upon by vinegar. Oils dissolve oxide of lead and become thick and consistent, in which state they are used as the basis of cements for water works, the vehicle for paints, and various other purposes. Sulphur dissolves lead in the dry way, and produces a brilliant and brittle compound, which is much more fusible than lead itself. Lead unites with most of the metals. Gold and silver are dissolved by it at a light red heat. Pieties forms a brittle compound with lead; mercury amalgamates with it, but the lead is again separable from it by mere agitation, in the form of an im palpable black powder. and lead do not unite without a strong heat; but the union of these metals is extremely slight, for at no greater heat than the melting point of lead it runs from the copper. Iron does not unite with lead in the metallic state. Tin unites very readily with lead, as already shown in the process of tinning lead pipes and sheets. The compound of these metals being very fusible, it is used as a solder either separately or both together. The mixture is made in various proportions : the best solder is said to be two parts tin and one part lead ; and the common solder, two parts lead and one part tin. Bismuth combines readily with lead, and affords a metal of a fine close grain, but very brittle. A mixture of eight parts bismuth, five lead, and three tin, malt at a heat below that of boiling water. Antimony forms a brittle compound with lead : see the article ALLOT. Nickel, cobalt, manganese, and zinc, do not unite with lead by fusion.