CONCRETIONS. 433 



solves readily in hydrochloric acid, from which it is precipitable 

 as an amorphous powder by ammonia; and if, after the am- 

 monia ceases to cause any further deposit, the filtered solution 

 yields a precipitate to oxalate of ammonia. 



b. It is basic phosphate of lime (which never occurs alone, 

 but is often associated with the salt which will be next con- 

 sidered) if it easily burns white but does not fuse, even under 

 the continued action of the blowpipe. It fuses, however, when 

 combined with the following salt (c), and its fusibility is pro- 

 portionate to the amount of the magnesian salt present : 

 consequently such a compound may be mistaken for the neutral 

 phosphate of lime. If it fuses before the blowpipe, and a solu- 

 tion in dilute hydrochloric acid yields a precipitate with am- 

 monia, which, under the microscope, appears in the crystalline 

 form represented in fig. 25 ; or if after the hydrochloric- acid 

 solution has been saturated with ammonia, and all the lime 

 thrown down by oxalate of ammonia, the filtered solution 

 again yields a precipitate to caustic ammonia; then it is not 

 neutral phosphate of lime, but the basic phosphate, in com- 

 bination with the following salt. With the exception of the 

 blowpipe test, the chemical characters of these two compounds 

 are similar. 



c. It is ammoniaco-magnesian phosphate (which usually 

 occurs in calculi associated with one of the preceding compounds) 

 if it develops a disagreeable ammoniacal odour before the blow- 

 pipe, and then fuses ; if it dissolves, without effervescence, in 

 hydrochloric and acetic acids, and, after the solution has been 

 nearly saturated with ammonia, is not affected by oxalic acid, 

 but is precipitated in the beautiful crystalline form represented 

 in fig. 25, by an excess of free ammonia. 



In proportion to the amount of basic phosphate of lime, 

 mixed with the ammoniaco-magnesian phosphate, the less 

 readily it fuses. 



d. It is oxalate of lime if it does not fuse before the blow- 

 pipe, if it easily burns white, and distributes a brilliant light; 

 if the heated specimen, when moistened with water, does not 

 dissolve, but exhibits a strong alkaline reaction, and dissolves 

 with effervescence in hydrochloric acid (or, if the heat has been 

 long continued and very intense, without effervescence) ; and 



ii. 28 



