154 PRACTICAL TREATISE ON THE MICROSCOPE. 



preventing any light from falling upon an opaque object, 

 except from the hole in the shade, in order that the light 

 on it may be contrasted strongly with the surrounding dark 

 medium. The author has used a shade of tinned iron, made 

 black on the outside with size and lamp-black, that answers the 

 same purpose as the shade of Mr. Holland ; but the plan of 

 raising or depressing the hole for the light to pass through he 

 did not adopt. 



Oil. — The best oil for burning in lamps is that known as 

 sperm. That obtained from the cocoa-nut is very cheap, and 

 gives a good light, but it has rather a disagreeable smell, 

 which is objectionable ; besides, it is very acid in its nature, 

 and lamps in which it is used should be either entirely made 

 of tinned iron, or, if of brass, they should be tinned in the 

 inside. Any lamp which burns this oil will be noticed to have 

 all brass work in contact with the oil speedily coated with 

 verdigris. The coromon solar oil will burn very well in the 

 fountain lamps, especially if the chimney be constructed like 

 that in fig. 105, but in all those with the flat reservoir it is far 

 too cloggy. Some persons are in the habit of burning a com- 

 mon kind of Florence or ohve oil, but it does not answer so 

 well as sperm, as, like the solar, it succeeds better in the 

 fountain lamps than in those with a flat reservoir. 



Jatropha Oil. — The author has lately been informed by his 

 friend, J. B. Estlin, Esq., of Bristol, that an oil, extracted from 

 the berries of a shrub of the genus Jatropha, found in the Cape 

 de Verd Islands, is used by all the microscopists in that city; it 

 burns well, gives a very bright light, and is perfectly free from 

 smell, it does not clog, but will keep pure in lamps for a very 

 long time; the only thing requiring attention is that the 

 lamp be warmed after it is trimmed before being lighted. 

 Messrs. Visger and MiUer, of Bristol, are the sole importers of 

 these berries and manufacturers of the oil, and the price, which 

 also is a recommendation, varies from 4s. Qd. to 5s. per gallon. 



Cleaning Lamps. — Lamps may be cleaned by nearly filling 

 the reservoir with a solution of caustic potash, and allowing it 

 to stand for a day or two, when aU the old oil will be con- 

 verted into soap. The potash can then be thrown out and 



