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The photographic news
- Bandzählung
- 27.1883
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- 1883
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1300, August 3, 1883
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- Titelblatt Titelblatt I
- Register Index III
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492 ITHE PHOTOGRAPHIC NEWS. [August 3, 1883. with this body. First, the lemon-yellow protoxalate must not be permitted to incrust the sides of the glass exposed to the light, and thus injure its transparency. Second, the solution of per oxalate must be kept nearly at a constant temperature, as its colour changes with the heat, it being at the freezing point emerald green, and at the boiling point brownish yellow. Third, before any carbonic acid can be disengaged, the solution must become saturated therewith ; and therefore, before the quantity of incident chemical rays can be correctly measured by the amount of disengaged carbonic acid, the portion dissolved must be removed either by exposing the solution to heat, or by passing a stream of hydrogen through it.” (To be continued.) SOLID AND LIQUID ILLUMINATING AGENTS. BY LEOPOLD FIELD, F.C.S.* The paraffins allow of substitution products with the haloids ; that is, they give up two atoms of hydrogen in exchange for an equal number of atoms of chlorine, bromine, or iodine. This is important, as the substitution compounds thus formed are iden tical with the additive compounds of the haloids, with the olefins ; which are the next series. These bodies have Cn H2n for their typical formula. Like the paraffins, they are colourless, readily inflammable, forming carbon dioxide and water. They are, how ever, much more easily acted upon by acids, and combine directly with the haloids. Here we have olefiant gas or ethylene, the first of the class burning with a flame much resembling that of methane. In this jar, inverted over water, I have two volumes of ethylene. Passing up from this bottle an equal proportion of chlorine, you will see the water, at first displaced, soon rise rapidly, while drops of an oily liquid collect in the apex of the funnel, whence they can be drawn off afterwards. This oily pungent liquid is ethylene dichloride, called of old, Dutch liquid. The name olefiant—oil making—is attributable to this property. The reaction, as before mentioned, is additive, and symbolised thus:— C,H, + Cl, = C,H,CI, ethylene chlorine ethylene dichloride which is identical with the substitution product formed by the action of chlorine upon methane. With the exception of cetene and cerotine, constituents of wax and spermaceti, the other olefines are of no interest to us. What renders ethylene of moment is the method of its formation from acetylene, the head of the third series of hydro-carbons, called acetylenes. The typical formula of these is Cn Han-2. We will only take acetylene itself, CH, Owing to the preponderance of carbon, you observe it burns with a smoky reddish flame. Though colourless, acetylene possesses a strong unpleasant smell, familiar to all who have allowed Bunsen burners to ignite below. In fact, as methane is always attendant upon slow decomposition of organic bodies, so acetylene is formed in every imperfect organic combustion. The feature of salient interest in its character is its production from the direct union of carbon and hydrogen. When a stream of the latter is passed over the carbon electrodes of a powerful battery, combination takes place, thus ;— C, + H, = c,H, acetylene Now, if nascent hydrogen act upon cuprous acetylide, we obtain ethylene, which combination we may depict simply as :— C,H,+H,=C,H, acetylene ethylene Again, by the action of sulphuric acid upon ethylene, ethylic alcohol, or spirits of wine, is formed : — 1. CH,+H,SOSOHC,Hs ethylene. 2. SO 4 HC 2 H 5 -|-OH 2 =H 2 SO 4 +C 2 H 5 OH sulphuric ethylic acid alcohol And as from ethylic alcohol most other organic compounds may be built up, we may be fairly said to have started ab ovo, and call acetylene the tap-root of organic compounds. I must not detain you now with the remaining hydro-carbons, the benzines, terpenes, &c., which are adduced as playing, or having played, * Continued from page 478. some part in the drama of lighting. Nor will we linger long over the alcohols, ethers, and acids, except for just such space as will give us an insight into the meanings and propriety of application of the terms. The alcohols owe their name to ethylic alcohol, the alcohol par excellence, our national beverage, commonly called spirits of wine. The word alcohol itself comes from the Arabic, al Icohol, antimony. This metal, very subtlely powdered, was applied as a pigment to the brows of oriental beauties. Soon any very fine powder was called alcohol. We find Boyle talking of reducing a body to a very “ subtile powder, or alcohol, as the chemists speak.” Ultimately, the epithet passed to all “ subtile ” bodies, and so to spirit of wine. The modern chemist, then, gave the name to a great order of com pounds, which stood respectively in the same relation to hydro carbons as ethylic alcohol does to its parent ethane ; from which it is formed by the substitution of OH, hydroxyl, for H. C,H, 1 tn —C,H, J n H,.- HU ethane, or etbylhydride=ethylic alcohol Ethylic and methylic {pebu, wine) alcohols have been used for illuminating ends, when tempered with some carbonaceous substance. Here is pure spirit, burning, as you see, non-lumi- nous ; and here some spirit in which camphor has been dissolved. This, you perceive, has a bright flame. But the sole use of methylated spirit to the chemist now is for heating ; the flame gives very great heat; as Boyle remarks—“In lamp furnaces wherein I have used spirits of wine for oil, the same flame has melted foliated gold.’’ The alcohol of chief interest to us, though not itself a luminant, is glycerine, of which later on. The ethers (aWu, I burn) may be regarded as formed from the alcohols, by the substitution of another radicle for H. In fact, the alcohols may be called the hydrates of the anhydride ethers, as in metallic compounds of the same nature. So we have ethylic ether, and ethylic alcohol, formed from ethane, which may, in its turn, be regarded as a hydride of the radical ethyl. The following arrangement gives a brief idea of the view which is taken of the formation of the whole chain, from the molecule of hydrogen to that of acetic acid. Hl . C 2 H 5 ) ,C 2 H 5 1 H) ' H, ' Hj U - hydrogen ethylhydride ethylhydrate (ethane) (alcohol) C 2 H 5 I 0 C 2 H 3 ) o .C 2 Ha CH,;°: H‘°: OH ethyloxide aldehyde acetic acid (ether) (alcohol dehydrated) Acetic acid is more properly regarded as being formed from methane, by substitution of— CO OH (carbhydroxl) for H : CH}+co-o=CObn } methane .. (methyl hydride) acetic acid Ether also is itself of no consequence here, but the compound ethers, as tallow and palm oil, will fully vindicate the brief attention we have paid the chief of their clan. The word acid originally meant a substance of a sour taste, which acted upon metals. Working upon the typical properties of the first definite acids, as sulphuric and hydrochloric, the name is now bestowed upon an infinite number of bodies ; their qualification being the possession of hydrogen atoms, which they can exchange for metals or radicles. Considering that every flower, berry, insect, animal, metal—in short, every body, animate or dead—furnishes a peculiar and distict acid, it is not surprising that the number is large. Of the substances with which we shall have to deal, cocoanut oil alone furnishes ten different acids, and bees’-wax three. There is an immense deal more to be said about the permuta tions and combinations possible between organic compounds. Time, and the fear of wearying you, forbid my pursuing the sub ject further. I have, however, drawn up a table of the chief changes mentioned. They are worth attention, as, by their aid, it is possible to furnish some explanation of the changes which nature brings about. Leaving now this arid but essential pre liminary, we will take a rapid retrospect of the art of lighting, see what materials our fathers had at their command, and how they used them. Probably the earliest known means of lighting was the toro, used largely of old in north countries, and still, no doubt, fight ing the Lapp and the Finn. This torch has been sent me from
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