PHARMACY. 



particles have no* time to arrange them- 

 selves, and are converted at once into a 

 confused or unvaried solid mass. Thus 

 glass, which when cooled quickly is so 

 perfectly uniform in its appearance, when 

 cooled slowly has a crystalline texture. 

 But in order to obtain crystals by means 

 of fusion, it is often necessary, after the 

 substance has begun to crystallize, to 

 remove the part which remains fluid; for 

 otherwise it would fill up the interstices 

 among 1 the crystals first formed, and give 

 the whole the appearance of one solid 

 mass. Thus, after a crust has formed on 

 the top of melted sulphur, by pouring 

 off the still fluid part we obtain regular 

 crystals. 



The means by which bodies which 

 have been disaggregated by solution are 

 made to crystallize most regularly, vary 

 according to the habitudes of the bodies 

 with their solvents and caloric. 



Some saline substances are much more 

 soluble in hot than in cold water. There- 

 fore a boiling saturated solution of any of 

 these will deposit, on cooling, the excess 

 of salt, which it is unable to dissolve 

 when cold. These salts commonly con- 

 tain much water of crystallization. Other 

 salts are scarcely, if at all, more soluble 

 in hot than in cold water; and, therefore, 

 their solutions must be evaporated either 

 by heat or spontaneously. These salts 

 commonly contain little water of crystal- 

 lization. The beauty and size of the 

 crystals depend upon the purity of the 

 solution, its quantity, and the mode of 

 conducting the evaporation and cooling. 



When the salt is not more soluble in 

 hot than in cold water, by means of 

 gentle evaporation a succession of pel- 

 licles are formed on the top of the solu- 

 tion, which either are removed or per- 

 mitted to sink to the bottom by their own 

 weight; and the evaporation is continued 

 until the crystallization be completed. 

 But when the salt is capable of crystalli- 

 zing on cooling, the evaporation is only 

 continued until a drop of the solution, 

 placed upon some cold body, shews a 

 disposition to crystallize, or at furthest 

 only until the first appearance of a pelli- 

 ole. The solution is then covered up, 

 and set aside to cool, and the more slowly 

 it cools the more regular are the crystals. 

 The mother-water, or solution which re- 

 mains after the crystals ure formed, may 

 be repeatedly treated in the same way, 

 as long ns it is capable of furnishing any 

 more salt. 



\Vhcn very large and beautiful crystals 



are wanted, they may be obtained by lay- 

 ing well-formed crystals in a saturated 

 solution of the same salt, andturning them 

 every day. In this way their size may be 

 considerably increased, though not with- 

 out limitation, for after a certain time 

 they grow smaller instead of larger. 



Crystallization is employed to obtain 

 crystallizable substances in a state of 

 purity; or to separate them from each 

 other, by taking advantage of their dif- 

 ferent solubility at different tempera- 

 tures. 



General Analysis resulting from the Appli- 

 cation of Chemical Powers. 



The simple elementary substances into 

 which bodies are capable of being re- 

 duced, submitted to chemical action, are 

 light, caloric, electricity, galvanism, mag- 

 netism, oxygen, hydrogen, nitrogen, 

 carbon, sulphur, soda, potash, phospho- 

 rus, metals, and earths. Of these the 

 first five have no appreciable gravity, 

 which is evinced by all the rest. Of the 

 latter, again, some are combustible, others 

 incombustible; some oxygenizable, others 

 destitute of all affinity for oxygen. But 

 to enter minutely into these subjects 

 would be to carry us beyond the limits 

 of this article, and to infringe upon those 

 that belong to chemistry as a general 

 science, and to which, as also to the seve- 

 ral articles above enumerated in the 

 alphabetical order, we refer the reader 

 for further information. So little pro- 

 gress, however, have we hitherto made 

 in the general science of chemistry, that 

 perhaps we are even now committing a 

 double error, in offering the above as a 

 table of simple elementary substances. 

 It is possible that not one of these sub- 

 stances is, strictly speaking, a simple 

 element, or, in other words, totally un- 

 compounded of rudiments that are more 

 simple. We may also be in an error in 

 conceiving every one of them to be a 

 distinct substance from every other: we 

 have many reasons, for example, for sup- 

 posing that galvanism and electricity are 

 the very same substance, only in different 

 states of modification ; and some philoso- 

 phers have ventured to suspect that 

 magnetism, or the magnetic power, is, 

 in like manner, in unity with both. Nei- 

 ther soda nor potash, again, are scarcely 

 any longer to be regarded as simple 

 substances; we have many valuable ex- 

 periments of Mr. Davy before us, by 

 which they appear to have been com- 



