46 iiYroNiTBiTES ; i'kopeuïies and tkepaeation by 



only necessary therefore, to s-ay something concerning the potas- 

 sium amalgam which is required, and of which as a reagent 

 little or nothing has heen published. 



Merely for convenience in working, the composition of the 

 potassium amalgam sliould correspond pretty closely, in parts 

 by weiglit, to that recommended for the sodium amalgam, 

 namely, (HgnK),, or 2800 mercury to 39 potassium, this l)eing 

 tlie weakest amalgam that is solid, and a pasty amalgam like 

 that of sodium not being obtainable. Although it crystallises 

 in simple cubes, often very large, whicli arc so sharp angled 

 that they can hardly be introduced into a liask without fractur- 

 ing it, the crystals are very easily crushed in a porcelain mortar 

 and are then in a state quite convenient for use. Sodium or 

 potassium amalgam, not stronger than here recommended (1 kg. 

 mercury to 14 grams alkali metal), is particularly easy to pre- 

 pare in Draper's way, that is, melting the sodium or potassium 

 under paraffin wax and adding the mercury to it, at first very 

 gradually. The operation can be performed on the open table. 

 When cold and Avanted, the amalgam is uncovered by cutting 

 through and lifting off the cake of paraffin and dug out with a 

 spatula. In spite of the fact that more heat is evolved, accord- 

 ing to Berthelot's numbers, the formation of potassium amalgam 

 is less violent than that of sodium amalgam. Potassium, also, 

 nearly always requires to be well stirred with a glass rod to 

 bring about its first contact with the mercury under the paraf- 

 fin ;=•= sodium never does. AVhen all the mercury has been 

 added, either amalgam requires good stirring in order to dis- 



* rroljably only liecaui^e tlie potassium presses so liglitly upon the incrcury on account 

 of its specific gravity Inot umcli exceeding that of the parallin, and not hecause of any 

 chemical difference. 



