880 ILLUMINATION 



ZCEZ.ATtiTD MOSS (Lichen tflslandc, Fr. ; Islandische Flechte, Ger.) is a lichen, 

 the Cetrarui Island-tea, which contains a substance soluble in hot water, but forming 

 a jelly when it cools, styled lic/miine. by M. Gu6rin. This moss is called in the 

 Pharmacopoeia Lichen hlandicus. It appears to have derived its name from the 

 circumstance that the Icelanders first discovered its medicinal qualities. Licheuine 

 is prepared by extracting first of all from the plant a bitter colouring matter, by 

 digesting 1 Ib. of it in 16 Ibs. of cold water containing 1 ounce of pearlash ; then 

 draining the lichen, edulcorating with cold water, and boiling it in 9 Ibs. of boiling 

 water, till 3 Ibs. be evaporated. The jelly which forms, upon cooling the filtered 

 solution, is dark coloured, but, being dried and redissolved in hot water, it becomes 

 clear and colourless. Lichenino consists of 39'33 carbon, 7'24 hydrogen, and 55'43 

 oxygen. The mucilage of Iceland moss is preferred in Germany to common paste 

 for dressing the warp of webs in the loom, because it remains soft, from its hygro- 

 metric quality. It is also mixed with the pulp, for sizing paper in the vat. For 

 several curious compounds obtained from Iceland moss, see Watts's ' Dictionary of 

 Chemistry.' 



XCEXiANX) SPAR. Crystallised carbonate of lime, of which the most beautiful 

 specimens are brought from Iceland. These are remarkable for their double refrac- 

 tion ; and hence this crystal is sometimes called doubly-refracting spar. 



XDOCRASE. A mineral known also as Vesuvian, closely resembling garnet in 

 chemical composition, but crystallising in the pyramidal system. 



XDRXAXiXXrE. A hydrocarbon occurring with cinnabar in the quicksilver mines 

 of Idria in Carniola. 



XDWAXiE-STONE. A peculiar Welsh hone-stone. It is obtained from the 

 older slate-rocks of the Snowdon district. 



XGXiESXASITE. A carbonate of lead and zinc, from Sardinia. 



XXiXXANTHXNE. A substance derived from the leaves of the common holly, 

 which might be employed for dyeing yellow. 



XXiXiOOPA OXXi. The produce of the Bassia longifolia, one of the most useful 

 trees grown in India. The oil might be denominated a butter, as it is solid from 

 82 to 84 Fahr., and liquefies at 90 to 95 Fahr. It is used in India for illumi- 

 nating purposes, and for the manufacture of soap. Samples of this oil were sent to 

 the International Exhibition of 1862, by the Singapore Local Committee. 



XXiXiUlWEXWATXOX. The means of determining the relative values of various 

 sources of illuminating power. 



It is often of the utmost importance that we should be enabled, with facility, to 

 determine the relative values of the light which we obtain from artificial sources. 

 The only way in which this can be effected, is by comparing with some standard 

 source of light the illuminating sources employed. Dr. Ure, who was on several 

 occasions called on to direct his attention to inquiries of this nature, instituted many 

 very ingenious and exact experiments ; to some of these it appears important that wo 

 should direct especial attention. Of the original paper on the cost of illumination, 

 many parts are now obsolete ; but, as much of it is still of considerable practical 

 value, the following selections have been made, all such being distinguished by 

 Dr. Ure's name. After many experiments to determine a standard, Dr. Ure says : 



'After comparing lights of many kinds, I find every reason to conclude that a large 

 wax candle, of three to the pound, either long or short, that is, either 12 or 15 inches 

 in length, as manufactured by one of the great wax-chandlers in London, and fur- 

 nished with a wick containing 27 or 28 threads of the best Turkey cotton, is capable 

 of furnishing a most uniform, or nearly invariable standard of illumination. It affords 

 one-tenth of the light emitted by one of the Argand lamps of the Trinity House, and 

 one-eleventh of the light of my mechanical lamp, when each lamp is made to burn 

 with its maximum flame, short of smoking.' 



Dr. Ure, however, for many of his determinations employed the French mechanical 

 lamp, known as Carcel's lamp ; and in connection with this the following remarks 

 occur : 



' Mr. Samuel Parker, long advantageously known to the public for his sinumbral 

 and pneumatic fountain -lamps, as well as other inventions subservient to domestic 

 comfort, having obtained a patent for a new lamp, in which the oil is hc.it cd by a very 

 simple contrivance, in the cistern, to any desired degree, before arriving at the uick. 

 I instituted an extensive series of experiments to determine its value in the production 

 of light, and consumption of oil, compared to the value of other lamps, as well as 

 candles in these respects.' 



Infiff. 1206, A, A, B, n, is a section of the cylinder which constitutes the cistern ; the 

 oil being contained between the inner and outer cylinders, and receiving heat from 

 the flame of the lamp which passes up through the inner cylinder, and is reverberated 

 more or less against its sides by the top of the metal chimney being notched and bent 



