in Zoological and Botanical Geography. 



15 



mary divisions of the earth into terrestrial Zoological and 

 Botanical regions, or whether such general divisions are 

 altogether impracticable. Some such simple classification 

 of regions is wanted to enable us readily to exhibit broad 

 results, and to show at a glance the external relations of 

 local faunas and floras. And if we go more into detail, 

 and adopt a larger number of primary divisions, we shall 

 not only lose many of these advantages, but shall probably 

 find insuperable difiiculties in harmonising the conflicting 

 distribution of the different groups of organised beings. 



On the Slaking of Quichlime. By John Davy, M.D., F.K.S., 

 Lond. and Edin.* 



In some experiments which I have made on the slaking 

 of quicklime, as its conversion into a hydrate is commonly 

 called, I have noticed certain results new to me, and as I can- 

 not find them noticed in any chemical work I have referred 

 to, I propose to give a brief account of them on the possi- 

 bility that they may be new to others. 



It is well known that as soon as water is added to and 

 absorbed by well-burnt lime fresh from the kiln, an imme- 

 diate union takes place, the mass becoming broken up and 

 falling into powder, with the production of much heat and 

 steam, t But if the lime has been kept exposed to the 

 air for two or three days, during which time it absorbs a 

 small quantity of water, J without at all disintegrating, the 

 same rapid union is not witnessed on the addition of water 

 sufficient to form a hydrate ; on the contrary, some minutes 

 will elapse before the combination takes place, and I find 

 there is a similar retardation of action from other causes 

 as shown by the results of the following experiments : — 



1. To a piece of lime taken from a mass, such as that 



* Kead at the Meeting of the British Association for the Advancement of 

 Science held at Newcastle. (1863.) 



t Gunpowder and sulphur have been ignited by it. See Annales de Chem. 

 et de Phys. xxiii. p. 217. About six pounds were slaked. 



X A little carbonic acid is absorbed at the same time, but this latter is not 

 essential, inasmuch as the lime exhibits the same peculiarity if kept in damp 

 air, excluding carbonic acid. 



