MINERALOGY. 



portant charafiers of minerals, and is obtained accu- 

 rately by weighing them in the hydroftatic balance. ( See 

 Hydrostatics. ) For moft praftical purpofes, a pair of 

 common gold fcales that ^vill turn freely with the tenth 

 part of a grain is fufBciently accurate. The mineral may 

 iirft be weighed, and the weight be noted, and then it muil 

 be fufpended by a fine thread, and weighed again in rain 

 or river water, about the temperature of 60"^. The original 

 weight of the mineral divided by the difference of the 

 weight will give its fpecific gravity, or the weight com- 

 pared with that of water. The heavieil bodies are the 

 metallic, and the metallic ores, which range from about five 

 times the weight of water to feventeen ; the latter is the 

 fpecific gravity of native platina. The heavieft earthy 

 minerals ai-e the barj'tic and ftrontitic earths, and the gems ; 

 thefe range from 3.5 to 4.5. The other falid earthy mine- 

 rals range from 2. to 3.5, and fome few folid nunerals are 

 lighter than water, as rock-cork. 



The feel, whether unctuous, or fmootli or dry, meagre 

 or harfh, is a charafler which ferves to diftinguifh particu- 

 lar minerals. The odour and taile are alfo characters of par- 

 ticular minerals ; fome yielding a peculiar odour naturally, as 

 petroleum, or when rubbed, as fwine-ftone ; and others, 

 as the faline, affect the tafte. Adhcfion to the tongue 

 is alfo a character polTefled by minerals which abforb water. 

 The coldnefs and found of minerals are alfo given as cha- 

 racters bv Werner, but they are of little pradlical value. 



Friable minerals are either loofe, as when the particles 

 have no perceptible coherence, or are (lightly cohering. 

 The particles are in fome inftances fcarcely difcernible, and 

 are called dufty particles, as in cobalt cruft ; in other 

 inftances, the particles are large and fcaly. 



The fluid minerals are few in number, and arc charac- 

 terifed by their fluidity, tranfparency, and luftre. 



The remaining charadters are purely chemical, except 

 the adlion of water, and of the atmofpherc, which is in 

 fome inftances chemical, and in others mechanical. Water 

 unites with many of the clays, and renders them plaftic ; 

 other minerals, as fuUers'-earth, fall to pieces in water, 

 without being diflblved, or even rendered plaftic. In fome 

 cafes, minerals abforb water, which alters their tranfparency 

 and colour. Saline minerals chemically combine with 

 water, and are diflblved. To the abforption of water, is 

 owing the property of adhering, when applied to the tongue 

 before noticed. The aftion of the atmoiphere on minerals 

 is principally efFecied either by the abftraction or abforption 

 of moifture, and the oxydation of minerals when expofed to 

 the air is for the moft part owing to the moifture which it 

 contains. 



The chemical charafters of minerals are thofe w hich the 

 mineralogift can afcertain by the aftion of acids, or of 

 heat as applied by the blow-pipe, either fimply or aided by 

 re-acrents. The aftion of acids is of great ufe in afcertain- 

 ing many eflential charafters of minerals. For this pur- 

 pofe, the muriatic or the nitric acids of moderate ftrength 

 are moft convenient. A minute fragment of the mineral 

 may be placed in a watch-glafs, and a few drops of acid 

 poured upon it. The native carbonates effervefce, and are 

 diflblved. Some minerals require to be reduced to a ftate 

 of powder to ftiew the action of acids, and are hereby 

 reduced to the form of jelly in a few hours, as zeolite. 

 Other minerals only require to be touched with a glafs rod 

 dipped in acid to afcertain their nature. 



The blow -pipe is an inftrument of very great ufe to the 

 mineralogift ; it has been already defcribed. ( See B^ow- 

 riPE. ) A blow -pipe which can be carried m the pocket, 

 to be worked when required by the mouth, is by far the 



moft convenient ; but it requirei fome precautions in the 

 management to render it efficient. The beft and cleareft 

 directions for this purpofe which we have feen are thofe 

 given by Mr. Aikin. 



" Few perfons," he fays, " are able at firft to produce a 

 continued ftream of air through the blow-pipe, and the attempt 

 often occafions a good deal of fatigue. I ftiallmakeno apo- 

 log\-, therefore, for treating this matter fomewhat in detail. 

 The firft thing to be done is to acquire the habit of breathing 

 eafily and without fatigue tlirough the noftrils alone ; then 

 to do the fame while the mouth is filled and the cheeks 

 inflated with air, the tongue being at the fame time flightly 

 raifed to the roof of the mouth, in order to obftruft the 

 communication between the mouth and the throat. When 

 this has been aequired, the blow-pipe may be put into the 

 mouth, and the confined air expelled through the pipe by 

 means of the mufcles of the cheeks. As foon as the air 

 is nearly exhaufted, the expiration from the lungs, inftead 

 of being made through the noftrils, is to be forced into the 

 cavity of the mouth ; the communication is then inftantly to 

 be fliut again by the tongue, and the remainder of the expi- 

 ration is to be expelled through the noftrils. The fecond, 

 and all fubfequent fupplies of air to the blow-pipe, are to 

 be introduced in the fame manner as the firft. Thus, with 

 a little practice, the power may be obtained of keeping up 

 a continued blaft for a quarter of an hour, or longer, without 

 inconvenience. 



" Much depends on the fize of the external aperture of 

 the blow-pipe. If fo large that the mouth requires very 

 frequent replenifliing, the flame will be wavering, and the 

 operator will foon be out of breath ; if, on the other hand, 

 the aperture be too fmall, the mufcles of the cheeks muft 

 be ftrongly contracted, in order to produce a fufficient 

 current, and pain and great fatigue of the part will foon 

 be the confequence. An aperture about the fize of the 

 fmalleft pin-hole will generally be found the moft convenient, 

 though for particular purpofes one fomewhat larger or a 

 httle fmaller may be required. 



" Several vai"ieties of form have been recommended for 

 the blow-pipe : they all have their advantages and difad- 

 vantages. Upon the whole, it appears defirable that there 

 ftiould be an expanfion of the tube fomewhere between the 

 two extremities, both for the fake of collecting and retain- 

 ing the condenfed moifture of the breath, and for producing 

 a regulated prefl"ure, and tlierefore a regular blaft. The 

 nofle alfo fliould be tipped with a moveable piece for the 

 convenience of giving at leaft three different fizes of aper- 

 ture. Thefe conditions being obtained, other circum- 

 ftances are of fmall importance, provided neither the bulk 

 nor weight of the inftrument be troublefome. 



" The fuel for this little reverberatory furnace (as the blow- 

 pipe apparatus may, without impropriety, be denominated) 

 is oil, tallow, or wax, kept in combuftion by means of a 

 wick. The oil is the worft, the tallow is better, and the- 

 wax is beft, not only as being cleaner, and free from any 

 offenfive fmell, but alfo as affording a greater heat. The 

 management of the wick too is a matter of fome nicety. It 

 ftiould neither be too high nor fnuffed too low, and (hould 

 be a little bent at its fummit from the blaft of the pipe. 

 All cafual currents and drafts of wind ought to be carefully 

 avoided, as rendering the flame unfteady, and very mate- 

 rially impairing its ftrength. The above conditions being 

 duly comphed with, the flame, while aCted on by the pipe, 

 will evidently confiil of two parts, an outer and inner ; the 

 latter will be of a light.blue colour, converging to a point 

 at the diftance of about an inch from the nofle ; the for- 

 mer will be of a yellowifti-white colour, and will converge 



lefs 



