ii. TEACHING (PURE). 507 



lavender with hydrochloric acid, and distilling with water 

 vapour. No solid modification seems to exist. 

 Formula C 10 H 16 2 HC1. 



Dr. E. A. Letts and Mr. James Davidson. 



2515. Sulphide of Potassium, obtained by allowing a very 

 concentrated aqueous solution (prepared in the usual way) to 

 remain at rest for some time. Sulphide of potassium is usually 

 stated to be red and uncrystallizable from water. 



Dr. E. A. Letts. 



2516. Mono-sodium Glycerine, obtained by mixing glycerine 

 with an alcoholic solution of ethylate of sodium. It contains a 

 molecule of alcohol (acting as water of crystallization), which it 

 loses at 100 C. 



(See Berichte der deutschen chemischen Gesellschaft, 1872.) 

 Formula C 3 H 5 (OH) 2 (ONa) + C 2 H 6 O. 



Dr. E. A. Letts. 



2517. Crystallized Pyro- sulphuric Acid, obtained by 

 adding the equivalent quantity of sulphuric anhydride to oil of 

 vitrioL 



Formula H 2 S 2 O 7 



Dr. E. A. Letts. 



2518. Pure Oxalate of Methyl, used for the preparation 

 of pure methyl alcohol. 



COOCH 3 

 Formula 



COOCH 3 

 Dr. E. A. Letts and R. M. Morrison. 



2519. Pure Methyl Alcohol, obtained by the action of 

 aqueous ammonia on the oxalate of methyl, and subsequent dehy- 

 dration with lime and sodium. 



Formula H CH 2 OH 



Dr. E. A. Letts and R. M. Morrison. 



II.-MODELS, DIAGRAMS, APPARATUS, &c. EMPLOYED 

 IN TEACHING PURE CHEMISTRY. 



2448. Drawings, two, illustrating the making of coal-gas, 

 used for teaching chemistry in the Secondary Schools. 



I. Coal-gas factory. 



II. Regulator of coal-gas factory. 



Dr. D. de Loos, Director of the Secondary Town School, 

 I^eyden. 



