102 



UNDULATORY FORCESLIGHT. 



[ILLUMINATING POWKH. 



grains of the strangest sulphuric acid, the following are 

 the in-.ml '< T ..f degree* raised by different oil* : 

 Olive oil . . C8Fah. Rape oil . . 100 Fah. 

 Luocaoil . . 72 Poppy oU . . 127 

 1 . . 72 ,, 



\\ ith au acid of IK) jvr cent., the rue in : 



i oil . . 64 Fah. ! Linseed oil . . 133 Fah. 

 Kpe oil ... 07 | 



Mixtures of these oils produce intermediate results. 



Aqua-fortis, or nitric ariti, acts with more or less 

 energy on the fats, and converts them into other acids ; 

 f which, namely, suberic acid, is a very constant 

 1 T.- i . '. Hut the most remarkable change is brought 

 about in all the fats by means of uiti-ous acid, or a solu- 

 tion of nitratt of mercury. Either of these compounds 

 will cause the fat oils to become solid ; the oleine of the 

 oil being converted into a semi-transparent jelly-like 

 mass, named elaidine. This curious change is effected 

 in olive, almond, rape-seed, hazel-nut, and other non- 

 drying oils; but the drying oils, as linseed, hemp- 

 seed, walnut, poppy, eke., are not affected by these 

 compounds. This circumstance, and tlio facility with 

 which the change is brought about, offer a means of dis- 

 tinguishing one kind of oil from another. M. Poutet 

 recommends the following method for the application of 

 this test : Dissolve six parts of mercury in seven and 

 a-half parts of nitric acid (sp. gr. 1'35); add two parts of 

 tliis solution to ninety-six parts of oil, and shake the 

 mixture every now and then for half-an-hour or so. If 

 the experiment be made on pure olive oil, it will congeal 

 in the course of seventeen hours in summer, or four 

 hours in winter. Other vegetable oils do not combine 

 so quickly with nitrate of mercury ; and the mixture 

 either remains fluid, or else the olive oil congeals, and 

 the other oil separates into a distinct layer. If the oil 

 has been adulterated with animal fat, the mixture 

 congeals in five hours, whilst the olive oil floats on the 

 surface, and may be decanted. MM. Boudet and Faure 

 have shown that this change is brought about by the hypo- 

 m acid contained in the nitrate of mercury. They 

 therefore recommend a solution of that acid in aqua-fortis 

 common nitrous acid does very well for the purpose ; 

 and they say that each of the fat oils takes its own time 

 to solidify, and develops its own colour. When one part 

 of hyponitrous acid is dissolved in nine of aqua- f ortis, 

 and then added to a hundred parts of oil, the colour 

 produced, and the times of solidification, are as follow : 



Colour. Time. 



Olive oil . . Greenish-blue . . 73 minutes. 

 Almond . . Dingy-white . . . 160 ,, 

 Filbert . . Greenish-blue . . 103 

 Acorn . . . Lemon-yellow . . 40 ,, 

 Castor . . (; olden-yellow . . 603 

 Colza . . . Yellowish-brown . 2400 

 Oil of poppies retards the solidifying effect, and this to 

 so great an extent, that when present in either of the 

 above, in no larger portion tlum 1 per cent. , it delays the 

 action for forty minutes. 



A mixture of equal parts of nitric and tulphurie acid's 

 also effects the coloration of the fixed oils ; and this has 

 been shown by M. Bc-hrens, as well as by MM. Guibourt 

 and lleveil, to be a good means for detecting the adulte- 

 ration of oils. About 150 grains of the mixed acids are 

 i like quantity of the oil, and the colour, which 

 is instantly produced, is as follows: 

 Oil of Sessama .... dark grass-green. 



olive light yellow. 



Linseed .... brownish-red. 

 Almond .... peach-blossom. 



Castor little changed. 



reddish-brown. 



l'"ppv brick-red. 



Gingilie 



o-seod . . . 

 Mustard . . . . 



Rape-seed (raw) . . 

 (refined) . 



rich orange-brown. 



rich chesnut-brown. 



orange-brown, 

 f orange- red, and then dirty 

 I i.Teen. 



red. and then pur- 



Oil of Cocoa-nut .... pale orange-red. 



Sperm whale . . . orange. 



,, Seal orange-brown. 



,, Cod-liver .... pinkish-violet. 



Tallow dirty brown. 



,. Net's-foot ... 

 M. Behrens states, that when olive oil is mixed with a 

 fourth part of its weight of sessama oil, it takes a beauti- 

 ful green colour; but Guibourt and Reveil assert, that it 

 will discover one-tenth part of sessama in oil of olive. 



Other oxydising agents, as chromic acid, or a satin-nfi-d 

 solution of bichromate of potash, in oil of vitriol, also act 

 in a very characteristic manner on the fixed oils. This 

 fact was first observed by M. Penot, who employed a 

 single drop of the latter solution with twenty drops of 

 oil, stirring them together on a white plate. The follow- 

 ing are the effects produced : 

 Almond oil . becomes yellowish in small lumps. 



Hemp-seed oil 

 Rape-seed oil . , 



1'oppy oil . . , 

 Ditto (cold-drawn) 

 Castor oil . 



yellow in clots on a green ground. 



Linseed oil . 



Nut oil . . 

 Olive oil . . 

 Cod-liver oil 



Whale oil . . 

 Tallow oil . 

 Neat's-foot oil 



,, white ground. 



slightly green. 



{brown clots on a white or green- 

 ish ground, 

 browu clots, 

 brown, 

 dark red. 



J brownish^red clots on brown 

 \ ground. 



reddish-brown. 



f brownish-red spots on brown 

 \ ground. 



The illuminating power of different oils varies with 

 different circumstances, as with the temperature of the 

 room, the size and form of the wick, and the freedom 

 with which the oil is supplied to the flame ; so that it is 

 difficult to arrive at anytlung more than an approxima- 

 tion to the value of different oils as illuminating ai; 

 Count Rumford estimated the relative illuminating 

 power of different oils when burnt in Argand and in 

 common lamps, thus the numbers being the weights 

 consumed to get au equal amount of light : 



Good wax, well-snuffed 100 grains. 



Olive oil in an Argand lamp . . . 100 ,, 

 Olive oil in a common lamp .... 129 ,, 



Rape oil ,, .... 125 



Linseed oil ...... .... 120 ,, 



From some experiments which have been conducted 

 for the purpose of arriving at an approximation to the 

 relative value of different oils, we have drawn up the 

 following table, which represents the proportions of oil 

 to be consumed in order to obtain a light of given value 

 namely, that of thirteen sperm candles, each consum- 

 ing 120 grains per hour. In these experiments the I 

 lamps were used for each of the oils, and the wick was 

 in each case of precisely the same description ; a new- 

 wick being employed for each experiment. The con- 

 sumption of oil in the Argand ranged between 316 and 

 378 grains per hour, and that of the common lamp be- 

 tween 87 and 123. 



Argand Lamp. Common Lamp. 



Tallow . . . 1008 grains. . . . 1300 grains. 



Sperm . . . 1029 . . . 17.M 



Train . . . 1067 . . . I'.'! I 



Olive . . . 1080 . . . -'on 



Seal ... 1107 . . . I*"- 1 



Sessama . . 1113 . . . irm 



Poppy . . . 1119 . . . I'< 10 



Refined rape . 1134 . . . 1881 



Refined linseed 1231 . . . 2370 



Haw rape . . 1 _':;<; . . . lino 



Brown rape . 1343 . . . 1827 



Mustard seed. 1 :'.M . . . '-'0.-.S 



i. ... 1302 , ... J!'7(i 



From this it will appear that there is im direct relation 

 between the illuminating power of the. oil and its con- 

 sumption ; for in some cases the oil burns better in the 

 common lamp than it does in the Argaud, and vice vend: 



