KEVIEWS. 



179 



We have never seen any elementary book on mineralogy — ever especially a dif- 

 ficult subject to simplify — in which so much really scientific gToimding was so 

 naturally and intelligibly put. The reader is first introduced to the forms of 

 minerals, then of crystals ; then to the characters of hardness, specific gTavity, 

 electrical and chemical qualities, &c. ; thence he is led to special mineralogy, taking 

 fii'st in order the precious stones ; then follow in due succession, the augitic 

 minerals, the felspatMc, micaceous, zeolitic, and the calcareous. Compounds of 

 baryta, of strontia ; salts of potash, of soda, of magnesia, of ammonia ; combus- 

 tible matters ; the metals and their ores. 



The following passages describing the use of the blow-pipe in mineral analysis, 

 will afibrd an example to our readers of the imassuming, easy, and simple, and 

 yet thoroughly scientific style in which the book is composed :— 



" As the pm'poses to wliich minerals may be applied, as well_ as the knowledge 

 of individual species, stand in very close relation to then- chemical composition, it 

 is important to acquire dexterity m the analysis of minerals ; and for this pui'pose 

 either the moist or diy method may be employed. The latter consists principally 

 in the use of the blow-pipe, the former in the solution of bodies in water, acids, 

 &c., and the application of certain re- agents by which precipitates of particular 

 colours and conditions are thrown down. In both cases the object is either to 

 obtain decomposition, or new combinations, which may once more be analysed. 



" In using the lloic-pipe, small fragments of the mineral may be held either on 

 charcoal or in platinum forceps ; so that, first, the fusibility, and then the 

 escaping vapoiu- or deposit left on the charcoal, as well as the residue, is examined, 

 either by reducing it in the inner flame, or by forming from it, along with borax, 

 soda, or salt of phosphorus, a pearl-like di-op, which is also to be considered with 

 reference to its colour and appearance. It is to be kept in mind, in using the 

 blow-pipe, that the point of the flame has an oxidizing power, and the inner blue 

 cone has a reducing influence, that is, it has the power of deoxidizhig ; also that 

 metals easily fused or reduced should not be held in the platinum forceps. Many 

 bodies, such as chalk, become exceedingly brilliant when heated, others colour the 

 flame at once, or after being held in it for some time. Thus, for example, all 

 calcareous minerals colour it vermilion-red, strontium gives a brilliant purple-red, 

 lithium a pale purplish-red, potassium a violet, sodium a pure hitense yellow, 

 baryta a green, boracic acid a pale green, acetate of copper a green, chloride of 

 copper a blue, and the presence of chlorine may be easily distinguished in this way 

 by the addition of some oxide of copper : while, on the other hand, the presence of 

 copper, be it of ever so small amount, may be easily recognized by the bright blue 

 flame on moistening the test with a drop of hydrochloric acid. The colour which 

 certain metallic oxides impart to a bead or pearl of borax, which has been obtained 

 by burning on charcoal, when heated on a platinum wire, is likewise important 

 Thus, the oxide of cobalt colom^s it blue, the oxide of copper imparts a gi;een 

 colour, and, if a gTanule of tin is added, it becomes red ; peroxide of iron 

 makes it yellow when hot, and ohve-gi'een when cold ; protoxide of iron gives a 

 grass-green, oxide of chromium an emerald-gTeen, oxide of manganese an ame- 

 thyst-red, oxides of manganese and u'on together give a blood-red or garnet-colour, 

 and so on ; while the oxides of zinc, lead, and bismuth do not change the colour of 

 the bead. Further details will be found in the description of the individual 

 minerals. The analysis by water is best performed in a closed glass-tube, or in a 

 small retort over a spuit-lamp, by which means smaU drops are deposited on the 

 colder part of the tube. This experiment serves at the same time to distinguish 

 the water from the carbonic acid, both of them producing small beads in the 

 borax pearl. 



"The presence of carbonic acid is best recognized int he moist way, by solution 

 in hydrochloric and nitric acids until effervescence takes place. Sulphur and sul- 

 phuric acid may be detected by using finely-powdered specimens along with soda 

 in the inner flame, by the aid of which a sulphuret of soda is produced, and this, 

 when moistened by a drop of water, and brought into contact with a silver coin, 

 leaves a brown stain, and gives off an odoiu- of rotten eggs (sulphuretted 

 hydrogen). 



" The presence of siliceous earths is best ascertained by melting the powdered 

 mineral along with borax or soda, while to the clear pearl which is formed there 



