618 PRINCIPLES OF CHEMISTRY 



decreases, 58 and therefore in the case of magnesium and beryllium, as 

 metals whose atomic weights are still less, we should expect the solu- 

 bility of the sulphates to be greater, and this is in reality the case. 



Just as in the series of the alkali metals we saw the metals potas- 

 sium, rubidium, and caesium approaching near to each other in their 

 properties, and allied to them two metals having smaller combining 

 weights namely, sodium, and the lightest of all, lithium, which all 

 exhibited certain peculiar characteristic properties so also in the case 

 of the metals of the alkaline earths we find, besides calcium, barium, 

 and strontium, the metal magnesium and also beryllium or gludnum. 

 In respect to the magnitude of its atomic weight, this last occupies the 

 same position in the series of the metals of the alkaline earths as lithium 

 does in the series of the alkali metals, for the combining weight of 

 beryllium, Be or Gl=9. This combining weight is greater than that 

 of lithium (7), as the combining weight of magnesium (24) is greater 

 than that of sodium (23), and as that of calcium (40) is greater than 

 that of potassium (39), &c. 59 Beryllium was so named because it occurs 

 in the mineral beryl. The metal is also called glucinum (from the 

 Greek word yXvxv's, ' sweet '), because its salts have a sweet taste. It 

 occurs in beryl, aquamarine, the emerald, and other minerals, which 

 are generally of a green colour ; they are sometimes found in consider- 

 able masses, but as a rule are comparatively rare and, as transparent 

 crystals, form precious stones. The composition of beryl and of the 

 emerald is as follows : Al 2 O 3 ,3BeO,6Si0 2 . The Siberian and Brazilian 

 beryls are the best known. The specific gravity of beryl is about 2'7. 

 Beryllium oxide, from the feebleness of its basic properties, presents 



58 One part of calcium sulphate at the ordinary temperature requires about 500 parts 

 of water for solution, strontium sulphate about 7,000 parts, barium sulphate about 400,000 

 parts, whilst beryllium sulphate is easily soluble in water. 



69 We refer beryllium to the class of the bivalent metals of the alkaline earths that 

 is, we ascribe to its oxide the formula BeO, and do not consider it as trivalent (Be = 13'5, 

 Chapter VII., Note 21), although that view has been upheld by many chemists. The true 

 atomic composition of beryllium oxide was first given by the Russian ehemist, Aydeeff 

 (1819), in his researches on the compounds of this metal. He compared the compounds of 

 beryllium to those of magnesium, and refuted the notion prevalent at the time, of the 

 resemblance between the oxides of beryllium and aluminium, by proving that beryllium 

 sulphate presents a greater resemblance to magnesium sulphate than to aluminium 

 sulphate. It was especially noticed that the analogues of alumina give alums, whilst 

 beryllium oxide, although it is a feeble base, easily giving, like magnesia, basic and 

 double salts, does not form true alums. The establishment of the periodic system of the 

 elements (1869), considered in the following chapter, immediately indicated that 

 Avde'effs view corresponded with the truth that is, that beryllium is bivalent, 

 which therefore necessitated the denial of its trivalency. This scientific controversy, 

 resulted in a long series of researches (1870-80) concerning this element, and ended in 

 Nilson and Pettersson two of the chief advocates.of the trivalency of beryllium deter- 

 fanning the vapour density of BeCl 3 (-40, Chapter VII., Note 21), which gave an 

 Undoubted proof of its bi valency 'see also Note 8). 



