356 Mr. Barthtt on propelling Vessels [Nov. 



The oxide of manganese made by means of chlorine hardly gives 

 any hyposulphate. Perhaps the oxide which we employed was 

 not at a maximum of oxidation ; and probably in this respect 

 there is a great difference between different oxides of manganese. 

 We have not been able to obtain hyposulphuric acid by treating 

 with sulphurous acid the hydrated peroxide of barium, or the 

 brown oxide of lead, though these two oxides present a compo- 

 sition analogous to that of peroxide of manganese. 



We shall conclude by stating the essential characters of 

 hyposulphuric acid, and of its salts. 



Hyposulphuric acid is distinguished from the other acids 'of 

 sulphur by the following properties : 



1 . It is decomposed into sulphurous and sulphuric acids when 

 exposed to heat. 



2. It forms soluble salts with barytes, strontian, lime, lead, 

 and silver. 



The characters of the hyposulphates are : 



1. They are all soluble. 



2. They only yield sulphurous acid when their solutions are 

 mixed with acids, if the mixture becomes hot of itself, or be 



a rtificially heated. 



3. They disengage a great deal of sulphurous acid at a high 

 temperature, and are converted into neutral sulphates. 



Article VI. 



On propelling Vessels by Means of Windmill Sails. 

 By J. M. Bartlett* 



It is but reasonable to conclude that the honour of inventing 

 steam-boats (now no less a subject of controversy between indi- 

 viduals than nations) will soon cease to occupy the attention of 

 mankind ; for since experience proves their inutility, except to a 

 very limited extent, reason very naturally rejects their adoption. 

 Nor is it to be wondered at ; for, whilst the expansibility of steam 

 . renders it a powerful agent, it makes it, at the same time, a 

 very dangerous auxiliary to the wants of man. f 



But it is not the insecurity alone, attendant on its operations, 

 which lessens the importance of steam, as a pVopeller of floating 

 , bodies ; many causes combine to render it either inefficient or 

 impractible. The fuel which would be required for a ^1 of 



♦ This paper was published, before in the Pamphleteer. We have been fritfuced 

 to insert it here that it may be "tarter known. The idea is not new. '>HS W AKpro- 

 jjosed nearly a century ago ; but I do not know whether it has been erer tried. — T. 



+ See the Minutes of the Evidence respecting Sttjpm^boals before a Select Com- 

 Jftittee of the House of Commons, in 1817. 



