MAG 



MAG 



2056. Also the same holds true down- 

 ward and upward ; as well as if taken 

 sideways to the middle, and back to the 

 same side again. Only one set of these 

 halfcliag-onals and their parallels, is drawn 

 in the same square upward and down- 

 ward; but another set may be drawn 

 from any of the other three sides. 5. The 

 four corner numbers in the great square, 

 added to the four central numbers in it, 

 make 1028, the half sum of any vertical 

 or horizontal column, which contains 16 

 numbers ; and also equal to half a dia- 

 gonal or its parallel. 6. If a square hole, 

 equal in breadth to four of the little 

 squares or cells, be cut in a paper, through 

 which any of the 16 little cells in the 

 great square may be seen, and the paper 

 be laid upon the great square ; the sum 

 of all the 16 numbers, seen through the 

 hole, is always equal to 2056, the sum of 

 the 16 numbers in any horizontal or ver- 

 tical column. 



MAGISTERY, an old chemical term, 

 very nearly synonymous with precipitate, 

 but is now rarely used, except in the 

 following combinations : magistery of 

 bismuth, which is the white oxide of 

 this metal precipitated from the nitrous 

 solution by the addition of water; ma- 

 gistery of sulphur, which is sulphur pre- 

 cipitated from its alkaline solution by an 

 acid. 



MAGNA charta. See LIBERTY. 



MAGNESIA, in chemistry, an earth, 

 the properties of which were not fully 

 known till Dr. Black, about the middle 

 of the last century, investigated its na- 

 ture. In the pursuit, the Doctor was led 

 to the important discovery of the carbo- 

 nic acid gas. Magnesia had, before his 

 time, been frequently confounded with 

 lime ; he, however, by the most accurate 

 experiments shewed that it possessed 

 properties different from all the other 

 earths. Although magnesia exists in 

 great abundance in combination with 

 other substances, it has never been found 

 perfectly pure in nature. It is an ingre- 

 dient in many fossils ; and several of the 

 salts, which it forms by combination with 

 the acids, are found in mineral springs, 

 and in the water of the ocean. Prom 

 these combinations magnesia is obtained 

 by different artificial processes. Mr. 

 Murray mentions the sulphate of magne- 

 sia, or Epsom salt, as well adapted to this 

 purpose. One part of this salt is to be 

 dissolved in twenty of water, and the so- 

 lution filtered ; to this is added, while 

 hot, a solution of pure potash or soda, as 

 kmg as precipitation is produced. The 



alkali combines with the sulphuric acid,and 

 the magnesia is separated : being insolu- 

 ble in water, \i falls down in white pow- 

 der : it is then washed in water till the 

 fluid comes off taste less. This earth ex- 

 ists under the form of a white spongy 

 powder, soft to the touch, without smell, 

 ami having a slightly bitter taste. Its spe- 

 cific gravity is 2.3. It slight!)' changes 

 vegetable colours to a green. Magnesia, 

 when quite pure, is infusible, though ex- 

 posed to the most intense heat : even in 

 the focus of the very powerful burning 

 mirror, or in the heat excited by oxygen 

 gas, it cannot be melted. When made 

 into a paste with water it contracts like 

 alumina, if exposed to a sudden heat. 

 It is almost insoluble in water. There is 

 no action between magnesia and hydro- 

 gen, or carbon, and very little between 

 it and phosphorus. It combines readily 

 with the acids, and with them forms neu- 

 tral salts. Of these the greater number 

 are soluble or crystallizible, and have a 

 bitter taste. It*does not enter into com- 

 bination with the fixed alkalies, but in 

 combination with some of the other 

 earths, it is fusible by means of a very 

 strong heat. With lime, in certain pro- 

 portions, it forms a greenish yellow glass. 

 It is much used in medicine as a gentle 

 laxative, and as an absorbent to destroy 

 acidity in the stomach. It is also employ- 

 ed to aid the solution of resinous and 

 gummy substances, as camphor and opium 

 in water. We shall notice only a few of 

 its combinations. 



Magnesia combines with sulphur either 

 in the dry or humid way, forming there- 

 by a sulphuret of magnesia. The solid 

 sulphuret of magnesia decomposes rapid- 

 ly when exposed to the air. 



Sulphate of magnesia is a compound of 

 sulphuric acid and magnesia, and is found 

 in sea water, and in many mineral 

 springs. Those at Epsom once afforded 

 a large part of what was used in com- 

 merce ; hence the name of Epsom salt. 

 Now indeed it is commonly obtained 

 from sea-water. The bittern water, or, 

 as it is usually called, the mother water of 

 common salt, that is, the water which 

 remains after the crystallization, con- 

 sists chiefly of sulphate of magnesia. 

 The constituent parts are, according to 

 Bergman, 



Sulphuric acid 33 



Magnesia 19 



Water 48 



100 



