106 RAPHIDES SIZE. [BOOK i. 



of various rhubarbs giving different feelings of grittiness to 

 the teeth when chewed, is said by Guibourt to be employed 

 as the test of their goodness. In the bulb of Scilla maritima, 

 not more than ten grains are contained in the same weight 

 of dried tissue. 



Size. The acicular vary exceedingly in their measure- 

 ment, some being not more than T -oVo P ar * of an inch in 

 length, whilst others will be as much as ^_. The conglo- 

 merate form is not subject to so much variation, varying only 

 from -^ to -g-i-g- part of an inch. The size of the rhombohedral 

 and other forms of crystals has no uniformity as to measure- 

 ment, some being not more than -g-oVo* whilst others are the 

 5*0- part of an inch. 



Composition. According to Raspail, the composition of 

 the acicular and conglomerate forms differs, the former being 

 phosphate, whilst the latter are oxalate of lime. Unger men- 

 tions that Buchner, Nees von Esenbeck, and others, have 

 found that their bases are sometimes lime, magnesia, and 

 silica, the latter not often occurring; and that these bases 

 are united to carbonic, oxalic, and phosphoric acids. The 

 whole of these assertions are more or less correct, but Raspail 

 has only given us negative proofs of their composition. It is 

 not difficult to obtain positive ones, by the following expe- 

 riments : 



If Raphides of the conglomerate form (perfectly free from 

 cellular tissue) be heated red hot, it will be observed that they 

 at first become black and again white, as the heating is con- 

 tinued to redness : in this state they readily dissolve in weak 

 nitric or hydrochloric acid, with effervescence; if to this solu- 

 tion oxalate of ammonia be added, a copious white precipitate 

 is obtained, which indicates that the base in this case has been 

 lime. In detecting the acid united with the lime, the pro- 

 ceeding is a little more complicated. For this purpose the 

 crystals are to be dissolved in dilute nitric acid, which occurs 

 without effervescence; to this solution nitrate of silver is to 

 be added, when a heavy white precipitate is produced, which, 

 when washed with distilled water to free it from any excess 

 of acid and nitrate of silver, is to be dried; if after this a 

 small portion be heated in the flame of a lamp it explodes, by 



