I815.J in the Physical Sciences. 37 



Phosphate of hme 'Jl'4 



Phosphate of magnesia S*2 



Carbonate of lime 40' I 



Carbonate of magnesia 35*G 



Carbonate of potash ] O/'O 



Sulphate of potash ^^"2 



Muriate of potash 15"2 



7. Gums. — Dr. John has published the result of liis experiments 

 on some varieties of gum which exude spontaneously from different 

 trees in (Jermany. 



a. Plum-giim. — The variety of plum known by the name of 

 Myrobala, whicli is yellow and round, when pricked by insects or 

 chopped, gives out a white clear sap, which gradually hardens into 

 gum. The constituents of this guni are. 



Gum arabic ] 2*5 



Cerasin 87*5 



100-0 



By cerasin Dr. John means a soft gelatinous matter wliich 

 remains 'undissolved when the gum is treated with water. It is 

 equally insoluble in alcohol ; but water acidulated with sulphuric 

 acid dissolves it in a boiling temperature. This substance has been 

 observed by Vauquelin, and by other chemists. It exists in the 

 cherry-tree gum of this country. 



I. Gum from the Stem of the Primus Avium, — Its constituents, 

 according to John, are, 



Cerasin 80 



Gum 20 



100 



Besides some traces of lime and potash in combination with an 

 acid. 



c. Sweet Chcrry-Tree Gum. — Its constituents are as follows : — 



Gum 5)7 



Phosphate of lime ~j 



Lime combined with a vegetable acid . . > 3 

 Potash combined with a vegetable acid . .J 



100 



I do not exactly know what Dr. John means by the sweet cherry. 

 The sweetest cherry which 1 know is the small black cherry whicli 

 grows wild abundantly in some parts of Scotland, and in that 

 country is called gccn. The gum from this tree I have examined, 

 and know tliat it contains a portion of Dr. John's cerasin. His 

 Kweet cherry, therefore, probably is the fruit of another tree. 



8. Starch. — Some years ago Bouillon Lagrange made the obser- 

 vation that when starch is roasted it acquires the property of dissolving 

 h\ cold wafer. Professor Diiberciner, of Jena, has published a set of 



