., 



OIKMISTKY. 



[t-IMK MAGNESIUM. 



vood'-n starea, sheds, earta, *e., are set fire to when a 

 bower of nun fall* on !> n them. Tho vnluo 



<f limo in mortar, consist* in the fact thnt it gradually 

 become* a compact *h<l, l>v the absorption of carl->nio 

 acid from UM air, for hi.'li it hai a great altr... 

 It in used by bVacher* lu a cheap determent ; and candle- 

 maken employ it to M|M>nify tallow in the process of 

 thestrarino manufacture. It is an essential constituent 

 of all soils ; and U found in almost every vegetable and 

 animal, in the form of either sulphate, carbonate, or 

 phosphate. In the process of tanning, it n used to re- 

 move hair from the skins ; and in notation an lime-water, 

 is a awful depiliatory for rumoring superfluous hairs 

 from the head and face. 



Chloride of lime, so called, is prodnced by passing 

 chlorine gas over slaked lime, by means of which the 

 gas unites with the earth, to form what is termed a hy- 

 poohlorite. The manufacture of this substance is carri-d 

 on to a large extent for the use of bleachers ; and per- 

 haps no chemical product is of more value to us, in a 

 social point of view, than this substance. By means of 

 its solution in water, as much cotton yarn or cloth can 

 be bleached in a few hours, as would have required weeks 

 under the old system of bleaching in the air. The pro- 

 cess is conducted as follows : The yarn is first boiled in 

 lime and water, to remove grease, resin, \c., and then 

 immersed in dilute sulphuric acid, to dissolve out the 

 oxide of iron usually present. It is then immersed in a 

 I'll solution of chloride of lime ; and having been taken 

 out and drained, it is dipped into a trough containing 

 acid and water, which sets free the chlorine. After 

 being washed in abundance of water, the yarn is then 

 dried; and will have acquired a perfectly white colour 

 during the process. Chloride of lime is much used also 

 as a disinfectant, for which it is extremely valuable. 



lame unites with chlorine, forming the chloride of 

 calcium. This sill-stance is much used in chemical 

 laboratories to absorb moisture. It is prepared by 

 saturating hydrochloric acid with lime ; and after evapo- 

 rating the water as far as possible, the crystals are fused 

 in a crucible. The chloride must be preserved from con- 

 tact with the atmosphere, or it will speedily become 

 liquid from the absorption of water. 



Fluorine and lime unite to form a fluoride, of which a 

 well-known mineral, fluor spar, is composed. This is the 

 chief source of fluorine and hydro- 11 none acid. The phos- 

 I !n.!.- of lime has been already described, under the head 

 of Phosphorus. * 



Sulphate of lime forms the well-known plaster of Paris. 

 It may be prepared by adding sulphuric acid to the car- 

 bonate ; but, on the large scale, it U produced by burning 

 the crystallised form of the salt, called gypsum. Its 

 use* are numerous ; amongst which, the most important 

 are that of producing a cement, and for making casts, 

 statues, Arc. It has a great attraction for water, and 

 so becomes solid on licing mixed with that liquid ; hence 

 its employment for the purposes we have referred to. 

 Crystals of the sulphate' nl>omnl in London clay, wherein 

 they may be readily distinguished by their glistening 

 appearance. 



"mi- acid and limonnito to form the carbonate, which 

 abounds in some part* of the world as chalk and lime- 

 stone. Chalk is the source whence lime is obtained ; .-mil 

 both are much used as a dressing for land Carbonate 

 of lime u found in both the vegetable and animal king- 

 doms in abundance. Although insoluble in pure water, 

 it is readily dissolved by water holding carbonic acid in 

 solution. It is the chief cause of the hardnuts of 

 water ; but it may lie removed by adding lime-water, 

 which precipitates the lime in solution as bicarbonate, 

 by seizing it* carbonic acid Dr. Clarke. <.f Ab< rrtoen, 



iiigeiiiouHly pro|>osed to apply this process for 

 li-i mi; hard water soft ; and it has been long in use at 

 I'lmrlton, near Woolwich, where, owing to the water 

 liemg iilii:iini-d fnnii the chalk hills, the wat 

 1 ' On boiling water containing chalk in solution, the 



,, I 



is deposited ; hence the cause of the fur in tea-kettles 

 stoani- boilers. Stalactites are formed by the drip- 

 BMI/, p. in. 



ping of water charged with the bicarbonate of lime, 

 through crevices in caves, A-c. , of which tin-re are nume- 

 rous instances in Derbyshire. The doubly refracting 

 Iceland spar, and the beautiful mineral Arragouite, are 

 both carbonates of lime. These may be generally found 

 in the crevices of limestone rocks ; and are produced by 

 crystallisation of the soluble carbonate, as it trick li-s 

 down their surface. Marble is a carbonate of lime which 

 has undergone fusion. If chalk be rammed into a gun- 

 barrel, and then exposed to an intense heat in a smith's 

 forge, it will present, on cooling, the appearance of mar- 

 ble. When pure, that substance is of a white crystalline 

 texture ; and the black or coloured veins in it are pro- 

 dnced by the presence of metallic oxides, especially that 

 of iron. 



Some of the most important salts of lime are the phos- 

 phates. They form, as we have frequently remarked, 

 an essential constituent of bone. Tho supcr-phos] 

 so called in commerce, is produced by adding sulphuric 

 uriii to cale : .ii'-d liniies, wiirii sulphate of lime is also 

 afforded. This is a valuable manure, and as such, is 

 highly prized by farmers. Cluann, and all animal excre- 

 nu'utitions substances contain it in considerable quan- 

 tities. A phosphate may be readily produced by adding 

 I'ii | 'hate of M n la to the chloride of calcium in solution. 



In medicine, lime, as a carbonate, the creta preparata 

 of the shops, is used as an antacid, which is also an ex- 

 cellent dentifrice. It is an essential ingredient in sea- 

 water ; hence the large quantities of chalk contained in 

 s. a shells. The eggs of all birds are chiefly composed of 

 it and albumen ; and it is a singular fact, that pod-bearing 

 vegetables bear no fruit in its absence; whilst in the 

 annual kingdom, birds will lay eggs without shells if 

 deprived of its use. 



MAGNESIUM. 



THIS metal forms the basis of the well-known earth 

 magnesia. It is obtained by heating potassium and 

 the chloride of magnesium together, in a test-tube or 

 crucible. At the moment that decomposition takes 

 place, both light and heat are evolved, and the metal 

 magnesium ifl set free. It has an appearance similar to 

 silver ; its symbol is Mg, and its equivalent 12'2. Ma-,' 

 in-sia is an oxide of the metal ; and is a somewhat abun- 

 dant earth. It is a constituent of many rocks, especially 

 of the magnesian limestone. Sea-shells also contain it ; 

 and as a chloride it is found in the water of the ocean. 

 In its pure state it is a white powder, scarcely soluble in 

 water, and belongs to the alkaline earths. Its chief 

 :e the sulphate, and carbonate. 



The sulphate is the well-known Epsom salts, so largely 

 employed in medicine. It is a constituent of many 

 mineral waters, and derives its name, from the town of 

 .u, in the wells near which it is found. It is ob- 

 tained by digesting sulphuric acid with magnesian lime- 

 stiim- : the solution being afterwards crystallised. 



The carbonate of magnesia, also used in medicine as 

 an antacid, is found abundantly in a native state, com- 

 bined with lime. The rocks formed of tin se materials 

 are termed dolomite ; and they are extensively used for 

 building purposes ; the new Houses of Parliament, and 

 many mlicr public buildings in London, etc., being con- 

 structed of it. When first precipitated, the carbonate is 

 a bulky white powder, which, on being heated, con tract* 

 considerably. The two kinds are sold in the shops as 

 light and heavy magnesia. It is soluble in excess of car- 

 lionii- a. id : and in that way can be obtained in crystals. 

 Mimay's lluid magnesia is prepared by dissolving the 

 carbonate in water containing carbonic acid in solution. 



Tin- chloride is produced by adding hydrochloric acid 

 to the carl- t. still better, by the addition of 



ammoniac to this solution ; when, after evaporation, it 

 is to be fused. It must be |,r. - i \od from access to air, 

 as it is highly deliquescent. As we before mentioned, 

 the nn-tal iKob'ained from this substance. 



Magnesia combines with nitric acid, forming a nitrate; 

 and with ammonia and phosphoric acid, it produces a 

 double salt, scarcely soluble in water. 



