COL 



COL 



ment. Thus, if the difference of 

 rature, between the heat-radiating sub- 

 stance and the atmosphere be 60 de- 

 grees, and if this raises the thermometer 

 45 degrees, the same difference between 

 the cold radiating substance and the atmo- 

 sphere will sink the thermometer 45 de- 

 grees, and so in proportion ; so that a 

 cold of 16 degrees will sink the ther- 

 mometer 12 degrees ; for 60 : 45 : : 16 : 

 12. 



Great degrees of cold are produced 

 by mixing together those substances 

 which dissolve rapidly . The reason of 

 this will appear, by recollecting what has 

 been said of the absorption of caloric, 

 when a solid body is converted into a 

 fluid. Mixtures to produce artificial cold 

 are generally made of the neutral salts 

 dissolved in water ; of diluted acids and 

 some of the neutral salts ; and of snow or 

 pounded ice with some of these salts. 

 A great number of experiments were 

 made upon this subject by Mr Walker; 

 also by Professor Lowitz, of Peters - 

 burgh ; by Fourcroy and Vauquelin ; and 

 by Guyton. The following table exhi- 

 bits he results of some of these experi- 

 ments. 



Table of freezing mixtures. 



J\'Rxtures. Thermom. sinks- 



Parts. 

 1. Muriate of am- "\ 



Water ... . 16J 



2. Muriate of am- "1 



monia ... 51 



Nitre 5 Mrom 50 to 3. 



Sulphate of soda 8 

 Water . . . . 16J 



3. Sulphate of soda 5} 



Diluted sulphu- Cfrom 50* to 0. 

 ric acid . . . 4 j 



4. Snow 1} 



Common salt 1 Cfrom 52 to 0. 



5. Sifow or pound- 3 



& lSV:v.--hft- 32 >-* 10 - 



7. Muriate of lime 3 ~) frQm ^o to 50 



8. Muriate of lime 2 1 from Q0 tQ __ 660 



10. Diluted sulpha- } 



ric acid. . . 10 Cfrom 68 t 91. 

 Snow . . . . . 8S 



When any of these substances are to 

 be employed as freezing mixtures, the 

 salts should be used fresh crystalized, 

 and reduced to fine powder ; and it will 

 perhaps be found most convenient to ob- 

 serve the proportions which are set dowu 

 in the table. Suppose it is wanted to 

 produce a degree of artificial cold equal 

 to 50, which is the temperature pro- 

 duced from 32 by the seventh freezing 

 mixture. The substances employed, 

 namely the muriate of lime and the 

 snow, must be previously cooled down 

 to the temperature of 32, or any de- 

 gree below it. This may be done by 

 placing them separately in the third 

 freezing mixture, the sulphate of soda, 

 and diluted sulphuric acid, which re- 

 duces the temperature from 50 to 30; 

 or in the fourth freezing mixture of 

 snow and common salt, which reduces 

 the temperature from 32 to 0. The 

 materials, thus cooled down, are then to 

 be mixed together as quickly as possi- 

 ble, when, if the experiment succeed, 

 the temperature will fall from 32 to 

 5(5, as in the seventh freezing mixture. 

 The vessels which are employed for 

 these processes should be very thin, 

 and made of the best conductors of 

 heat. Vessels of tin plate answer the 

 purpose, and when acids are to be used 

 they may be lined with wax, which 

 will secure them sufficiently against 

 their action. They should be of no 

 larger dimensions than just to contain 

 the materials. 



COLDENIA, in botany, so called in 

 honour of C. Golden, a curious botanist 

 of North America; a genus of the Te- 

 trandria Tetragynia class and order. Na- 

 tural order; Asperifolix. Borraginex, 

 Jussieu. Essential character : calyx four- 

 leaved ; corolla funnel formed; styles 

 four ; seeds two, two-celled. There is 

 but a single species, viz. C. procumbens, 

 a annual plant, whose branches trail on 

 the ground ; they extend nearly a foot 

 from the root, and divide into many 

 smaller branches. It is a native of the 

 East Indies, but has been cultivated here 

 for half a century. 



COLEOPTERA, in natural history, an 

 order of insects, which includes all those 

 whose wings are guarded by a pair of 

 strong, horny, exterior cases or cover- 

 ings, under which the wings are folded 

 up when at rest. In common language 

 these insects are called beetles, though, 

 in reality that term is now restricted to 

 the Scarabaeus genus. The wing-sheaths, 

 or horny coverings, are sometimes called 

 coleoptera, but more generally elytra. 



