Volatile power of liquids

Aug., 1~80.1

137

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m be printed. The thlekncs~ ~,t' ~}w zim. pJar~ u~,~,~ is fi~,,m i!! I,~ inch. The same process of zinc (m,_,'raving as "~bov- des~'ribed cmJ also by: employed for the l)rodm'ti,m (,i' am" sut!ject, a piclur~ ,,t" wbi(.h is pro(lucetl on the zinc in other ways thau /)~ lithography. Thus transt>rs from a steel or eopper engraved plate ,,r a photo~'raph (:an b~, produ<,(;(l, the latter on a speei'dly prepared zhw surtiu'% or a sketch may be made on the zinc direct with lith~'raphi<, ink or chalk. Simple am this l>r(>eessapli>ears, it requires <.~mslder'd~h, skill and ear~: cm the part of the operators to pro, huce really good result% but some excellent specimens of ldoeks, as well as prints from th,~ same, mar b~, seen at the show.., or at :my time in the (~Oltlllll|s Ot* I[]liS .iournal, our line engravings bcing prepared c:xclusivclv in this maturer. The at:q~lications of this process are very various and widespread, and the advantages it possesses over line wood mlgraving are mazfif(st. ~he simplest sketehes, or the most complicated drawings covered with dime,Jsions and writing, are produced with almost equal t~tciliD,; tim-similes of ancient inscriptions, manuscripts, etc., ~;m be photog'raplled diro't upon zinc, and require practically n,, hand labor, so that :tbsolute accuracy is obtained. "l']lese are only a few applieati(ms, but are sufficient to show that the process is superior in many respects to the much older art of wood engraving, althoug'h it must alwavs remain inferior to it where e~bvts of color are required.

V o l a t i l e :Power of 1:,iquids.- Pietet gives a general equation, drawn directly from the mechanical theo W of heat, which embraces all Regnault's equations of interpolation fi~r all known volatile liquids; in or.her words, it gives the maximum tension of any givetl vapor at any given temperature. Let 2 be the latent heat of wdatilizaLion at a temperature t/ c tim specifi(" heat of the liquid; k the specific heat of the vapors; P the maximum tension of the vapors at temperature t; 3 density of the vapors, varying according to the law of the co-volumes" / -~"(*"~' a specific' integral deduced fr, m~ the work '

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clone, in accordance with Marlotte's law. Theil . . . . . .[. 2. .'. . - - (e - k} (e' .... 0 ] c31 ;4 2/~, I

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1-2~3 ,; (t I

-

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1i,:3:3a,27.i ~i ,'-i~ 5.<~-7~..............

--Compte, lle~.b~s. WHOLE No. VOL. CX.---(THJI~b SEf~I~:S, V,,I. ]xxx. !

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