Chap. 9.]
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difficult forms, and such as require the metal of different thickness in thesame piece.®—(See L’Art du Vitrier, pl. v, Arts et Metieres.)
It has long been known that water conveyed through leaden pipes be-comes more or less impregnated with a poisonous solution of that metal;a fact of which the ancients were fully aware, and which made them veryscrupulous in using it for purposes of domestic economy. Hippocrates and Galen denounced its employment both for cisterns to contain, andtubes through which to conduct water. Ancient architects were of the sameopinion ; thus Yitruvius observes, that water drawn from leaden tubes isvery pernicious, and adds, “ we should not, therefore, conduct water inpipes of lead if we would have it wholesome.” The Medical Transactionsof modern times, and works on mineral poisons abound with examples ofthe fatal effects of drinking water from reservoirs and pipes of this metal.
Several modes have been devised to render leaden pipes innoxious. In1804, an English patent was obtained for coating their interior surfaceswith tin. This was effected in the following manner :—Suppose a work-man engaged in making tubes of half an inch bore ; he first pours lead intoan iron mold and forms a pipe two feet long, an inch thick, and nearly aninch in the bore : as soon as the lead poured in becomes solid, he with-draws the Steel mandril which formed the interior of the tube, throws ina little rosin dust, and inserts a half inch mandril, between which and theinside of the tube a certain space is left. Into this space he then poursmelted tin, which as it collects below, causes the rosin to float on its sur-face, as it rises to the top, and lubricates the hot sides of the leaden tube.Both metals thus become United, and when the tin becomes solid the man-dril is taken out; and the tube, thus plated with tin, is passed to the draw-bench, and drawn out to the required length like an ordinary leaden tube.There is some difficulty in making the tin unite uniformly to the lead, andwhen this does not take place the pipes are apt to be broken in drawing;for as the two metals do not Stretch equally, the thin lining of tin is pulledapart; and if the lead does not separate at the same place, its surface isexposed, and the strength of the tube greatly diminished at such places.—(Repertory of Arts, 2d series, vol. v.)
In 1820 another English patent was issued for a similar plan, the dif-ference consisting chiefly in a mode of better securing the Union of the tinwith the lead.—Ibid. vol. xxxviii.
In 1832, the author of this volume took out a patent for coating leadenpipes with tin, by passing them, after being drawn and otherwise finished,through a bath of the fluid metal. As there is a difference in the fusingpoints of tin and lead of about 200° Fahrenheit, there is no difficulty in theprocess. By this plan tubes are effectually tinned both inside and out, andany imperfections or fissures are soldered up. The Operation is exceed-ingly simple and the expense triffing. The process is patented in England,where the tubes are, we believe, more extensively used than in this coun-try.—(See Journal of the Franklin Institute for November, 1832, andMay, 1835.)
Valves and Cocks are too essential to hydraulic engines to be omittedin this work. The principle of the valve has always been in use for avariety of purposes. Doors are valves, and were so named by the ancients.Those of the private apartments of Juno were contrived by Vulcan to closeof themselves. Thus Homer sings :