APPENDIX. 307 



are either, I, Hard. 2. Semihard, or, 3. Soft. VI. With 

 respect t*o Tenacity, minerals are, 1. JBrittle, when on being 

 cut with a knife the particles fly away with noise ; 2. Sectile, 

 when the particles do not fly off but remain ; 3. Ductile, 

 when the mineral can be cut into slices. VIJ. By Frangi- 

 hility is meant the resistance which minerals make when 

 we attempt to break them. The degrees are five, 1. Very 

 tough ; 2. Tough ; 3. Moderately tough ; 4. Fragile ; 5. 

 Very fragile. VIII. With respect to Flexibility, some are, 

 . 1. Elastic; others, 2. Common; others, 3. Injlexible. IX. 

 Some minerals adhere to the tongue, 1. Very strongly ; 2. 

 others moderately ; 3. others slightly ; 4. and others very 

 slightly. X. Some minerals give a ringing sound ; others 

 a grating sound ; others a creakiug sound, as tin. 



With respect to electricity, some fninerals become electric 

 when heated, others when rubbed, others cannot be rendered 

 electric. The electricity of some is positive, of others nega' 

 tive. 



LESSON 79. 



Silver and Mercury. Freezing mixtures. Salts dissolved 

 in water, ice, or snow dissolved in nitric and muriatic acids, 

 reduce the temperature of the mixtures a great number of 

 degrees. Mercury has been frozen or rendered solid, even 

 in summer, bough it requires the temperature of 39° below 

 zero at least .o congeal that metal. Four parts of caustic 

 potash, crystallized, and reduced to a fine powder, mixed with 

 three parts ofsnow sinks the mercury in a thermometer from 

 32^ above to 51° below zero. Two parts muriate of lime 

 mixed with one of snow, sinks it from zero to 66° below 

 zero. The cause is, that the mixture has a larger capacity 

 for caloric than would be derived from blending the two ca- 

 pacities of the ingredients, and taking a mean proportional 

 between them. 



LESSON 91. 



Roots, Stems, Buds and Leaves. The generality of roota^ 

 may be arranged under the following heads. 1. A Fibrous 

 Root, consisting only of fibres either branched or undivided. 

 Many grasses and the greater part of annual herbs have this 

 4tind of root. 2. A Creeping Rootf as in Mint. 3. A Spin^ 



