July 27, 1883. | THE PHOTOGRAPHIC NEWS. 477 SOLID AND LIQUID ILLUMINATING AGENTS. BY LEOPOLD FIELD, F.C.S.* You who come from stations lighted by electricity, and through streets brilliant in gaslight, may find good cause for wonder that so much can be found to be said upon out-of-date subjects like the lamp and the candle, which are the simple equivalents of the title of these lectures. The system according to which I have concatenated the various bodies used for lamps and candles is based upon the theories held by the generality of modern chemists. The diagram shows how every member almost of these myriad—these Mormon —families can be assigned to one or the other of the four groups —hydrocarbons, alcohols, ethers, and acids. Hydrocarbons may be regarded as parents of the others, which in theory, borne out to a certain extent by experiment, are derived from them by more or less complicated processes. As their name implies, the hydrocarbons consist entirely of hydrogen and carbon. The relative proportions of these elements in the different series vary by equal increments. First on the list, as to us they are the most important, come the paraffins. The white solid familiar to us under that denomination consists of a number of the higher CO «4 bD co ci ci Pl a a a •c a M e g a a aS cl 8 fl fl I •a a •c s 8 4 2 PQ 72 ad W Em o,-- mHe Bo rV o o o 8 Ee FA 71 d DO 5 a %E 4 a a 2,8 E C Pd co ci dualised. * Jox^rnal of the Society of Arts, fl o Ps P fl O P- N 11 oo ai <1 a w H 6 c 6 O = M ei 3 # K E S s 8 E 00 U 93 F 4- E E i E s In co E fl ci fl tn 2 W o 9 = « 2 o5 0U .o c o 8 II 4 + 19 EE oo s o E tn a ■J: * : ’o •2.8 EE. AO o b I W CM w co gg# • tn o 72 E # N 5 $8 e + " 8 03 HE • 8 II < M <n 38 8 H S 2 § S “ -8-3-8 = E • m #Mm- 2 FF 5°4° b23 too E o 3 8 346 8E °8° 58 o E E 0 ’9 2 Qa S 6m . — m m 3 9 2 B Pm •8 88§ cEZ 3 o, — 18 5 3a They all conform to one typical formula, Cn Hau +2. and are all very inert, characterless compounds, to which qualities they owe their name (parum, little, akin). The first of the twenty has long been known—it is the joy of the lecturer, as methane ; the wonder of the bucolic, as marsh gas .EE 50 5 Ee B, homologues of this series, the compositiou of which is so nearly identical as to defy the most cunning attempts at isolation. At the present time, twenty well defined paraffins have been indivi- #$2.84. 288288 aco_c2 Cl OOOOO Cl co + a 0 n • • fl « EmEE 3m co •Q P O x fl ‘9 - « 5 2 r E HH. H,