NORTH UIST. PEAT. 131 



causes affecting the temperature or moisture of the 

 atmosphere. The properties of peat as a fuel vary accord- 

 ing to those circumstances ; the best being that of which 

 the decomposition is most complete and the specific 

 gravity and compactness greatest. Such is the case in 

 that of North Uist which has given rise to these remarks. 



As the growth of peat necessarily keeps pace with that 

 of the vegetables from which it is formed, it is evident that 

 the cessation of the one is implied in that of the other. 

 Hence the necessity, now at length understood, of re- 

 placing the living turf on the bog whence peat has been 

 cut ; a condition now required in all leases where liberty 

 to cut it is included. No vegetable seems willingly to 

 attach itself to pure peat ; and thus a bog once bared to a 

 sufficient depth remains naked : where the decomposition 

 is but incipient, the process of vegetation is renewed and 

 continued without difficulty. 



The solubility of peat in water varies according to the 

 degree of vegetable decomposition: pure peat communi- 

 cates no stain, and the brown water that contaminates 

 the rivers of the Highlands is derived from it in the 

 incipient stage of the process. The cause of this will 

 appear from considering the nature and progress of the 

 chemical changes ; on which I shall bestow but a few words 

 as they are abundantly simple ; although, like the rest of 

 the history of this substance, much misunderstood. 



If recent vegetable matter be distilled carefully by a 

 red heat, it is converted into charcoal, acetic acid, and 

 an oil varying in density according to the stage of the 

 process, together with an occasional small quantity of 

 ammonia. No inflammable gas is produced but by 

 mismanagement of the operation. It is unnecessary to 

 describe these results more particularly, as I have treated 

 of them at some length in the 2d Vol. of the Geological 

 Transactions. There is in this case a certain proportion 

 between the coal and the oil. This latter substance, under 

 its various modifications of pitch, tar, or essential oil, U 



