442 On separating the Phosphates of Lime and Magnesia. 



and conversely, is to be preferred to others in its application 

 to the pendulum ; for, by thus allowing a proportional increase 

 in the extent of vibration, due compensation for changes in 

 the density of the air is obtained ; besides, by the use of the 

 thin spring or knife-edge, instead of a thick adjusted spring, 

 the liability to changes in the rate of the pendulum from that 

 cause is removed. If good workmanship be not spared, and 

 a dead-beat scapement with jewelled pallets be employed; 

 and if the impulse be given in the middle, which can easily 

 be done by slightly hollowing the impulse flanches ; and if the 

 pendulum, which must at least be 8 or 10 pounds in weight, 

 be firmly fixed, — the maintaining power may be transmitted 

 without any material diminution for a period of several years. 

 The changes which arise from increase of friction, and cause a 

 decrease of vibration, are but small as well as slow in their pro- 

 gress, and they can be easily calculated upon ; but the changes 

 which arise from the state of the atmosphere are frequent, and 

 to estimate them properly is a much more difficult task. 

 Glasgow, 1833. 



LXXII. On separating the Phosphates of Lime and Magnesia. 



By Mr. G. O. Rees.* 

 ~11I7"HEN the phosphate of lime occurs in urinary calculi 

 ** mixed with the phosphate of ammonia and magnesia, 

 it is rather difficult to discriminate between them. I have, how- 

 ever, found the following process to answer this purpose per- 

 fectly. 



Heat two or three grains of the calculus to be examined to 

 redness, so as to expel the ammonia present, which if allowed 

 to remain would interfere with the future steps of the process 

 by forming a triple salt. The residue is to be dissolved in 

 dilute hydrochloric acid, and a solution of bicarbonate of 

 potassa added in excess ; part of the base of the phosphate, 

 whether of lime or magnesia, is now held in solution as bicar- 

 bonate, and may be procured as carbonate by filtration and 

 boiling. The carbonate so precipitated must be well washed, 

 in order to free it from the phosphate of potassa, and may 

 then be dissolved in dilute hydrochloric acid ; by these means 

 the phosphoric acid is entirely expelled from the earths, and 

 their usual tests now act characteristically. Thus if magnesia 

 be present, ammonia produces a precipitate soluble in a solu- 

 tion of muriate of ammonia; if lime be in the solution, oxalate 

 of ammonia precipitates it; and if both earths be present, both 

 these indications are fulfilled. 



* Communicated by the Author. 



