METALS AND METALLOIDS 701 



thallic diethyl hydroxide, T1(C 2 H 5 ) 2 . OH, a strongly alkaline 

 base. 



Thallium diphenyl bromide, Tl(C 6 H 6 ) 2 Br, is an example of an 

 aryl derivative obtained through the agency of the Grignard 

 reaction, a process which is explained in the following section. 



(c) The Glucinum Family 



In the vertical periodic series containing the typical bivalent 

 metals we come across a family possessing in a very marked 

 degree the property of yielding organic derivatives. This is the 

 glucinum family, including zinc and mercury, the organic 

 derivatives of which have already been discussed. 



The other natural family of this series contains the metals of 

 the alkaline earths and radium : 



Gl Mg Zn Cd Hg 



Ca Sr Ba Ra 



The organic derivatives of calcium have been mentioned as 

 substitutes for the corresponding compounds of magnesium in 

 the Grignard reaction, but do not appear to have met with any 

 considerable degree of success. Very little is known concerning 

 the organic derivatives of strontium and barium, the metals of 

 the alkaline earths showing little or no tendency to combine 

 with hydrocarbon radicals. Radium is the final member of this 

 family, and it therefore seems unlikely that organic derivatives 

 of this remarkable element will be readily obtained. 



In the glucinum family cadmium shows the least tendency 

 to unite with hydrocarbon radicals. Cadmium dimethyl and 

 diethyl have been obtained, but only in very small yield ; they 

 are fuming liquids spontaneously inflammable in air and 

 energetically decomposed by water. 



The glucinum compounds are prepared by the interaction of 

 this metal and mercury alkyls. Glucinum dimethyl and diethyl 

 are fuming liquids decomposed by water but not spontaneously 

 inflammable in air. 



The Grignard Reagents. — To the early workers in this field 

 the organic compounds of magnesium did not appear to be very 

 promising materials for synthetic purposes. But as the result of 

 modern researches, all carried out within the last thirteen years, 

 the organo-magnesium derivatives have proved to be the most 

 general synthetic agents hitherto discovered in organic chemistry. 



In 1899 Barbier found that a mixture of magnesium and 



