112 DEXTEINE. 



odour will be given off, and the cystine will burn off 

 without melting, evolving a smell of hydrocyanic acid. 



Dentine. 1. The main portion of the substance of 

 the teeth, covered outside by the enamel. The struc- 

 ture is tubular. It contains animal matter, calcium 

 carbonate and phosphate, and a trace of magnesium 

 phosphate. 



2. The enamel contains calcium carbonate, phosphate, 

 and fluoride, magnesium phosphate, and a very little 

 organic matter. 



Dextrine, C 12 H 10 10 . 1. Take 20 grammes of starch, 

 mix with 30 c.c. of water. Dilute 5 grammes of con- 

 centrated sulphuric acid with 30 c.c. of water and add 

 the dilute acid gradually to the starch paste. Mix 

 well and heat for some time in a water bath at 90 C. 

 "When cold add alcohol ; the dextrine will be precipi- 

 tated. 



2. Dextrine cannot be crystallised ; it is soluble in 

 water, but insoluble in absolute alcohol. 



3. Dissolve a portion in water and add a drop of 

 dilute tincture of iodine; the solution remains un- 

 coloured. Starch, under similar circumstances, would 

 be coloured a deep blue. 



4. Add to an aqueous solution of dextrine, some 

 solution of caustic potash and a drop of a very dilute 

 sulphate of copper solution ; boil ; the copper salt will 

 be reduced, the liquid darkens, and finally a bright red 

 precipitate of copper suboxyde is precipitated. 



5. It rotates polarised light to the right. Boil dex- 



