406 Miscellaneous Intelligence. 



ently heated matter in the same state, whether solid, liquid, or 

 gaseous, quickly exchange temperatures. But the steam and water 

 in an engine-boiler, though containing very different quantities of 

 heat, remain in contact without any such tendency. Water can, 

 therefore, be supplied to the vessel in which it is to be evaporated, 

 before it can expand into steam, which would oppose its own 

 entrance ; while a quantity of already existing vapour could not be 

 introduced without great difficulty. Even when the supply of water 

 requires the aid of a force-pump, as in high-pressure engines, the 

 water (having a bulk five hundred or a thousand times less than 

 that of the vapour it is to form) demands a very small expenditure 

 of power, as compared with the introduction of one measure of gas, 

 which is to be expanded only into two. 



" These remarks are offered with great deference to the author 

 of the best epitome of natural philosophy in the English language. 

 But the subject of steam-power is just now so exciting, and the 

 alleged possibility of increasing fourfold the resources of Great 

 Britain is so startling, that you will perhaps think this hasty criticism 

 may tend to elicit a confirmation of what would be an inestimable 

 idea, or else to guard against the ruinous attempts which might 

 be induced by a flattering but delusive speculation. 



M I am, Sir, your obedient servant, A. A." 



18. — Cement from Iron Filings. By M. Miallre. — Having re- 

 flected about a year since upon the action of vinegar in the pre- 

 paration of the cement known as mastic de limaille, which is 

 prepared in this way — iron filings, garlic, and vinegar, of each a 

 sufficient quantity to form a mass of moderate consistency ; I pro- 

 posed to substitute sulphuric acid diluted with water, for the vinegar, 

 in the proportion of one ounce of acid to a litre (a little above two 

 pints) of water, and to reject the garlic as useless. This alteration 

 was soon adopted by all those to whom I communicated it ; for 

 vinegar generally costs in Paris eight or ten sous the litre, while 

 the price of the acidulated water does not amount to as many 

 centimes. Thus an architect, to whom I had made it known, assures 

 me that this change, which at first appeared to merit no attention, 

 will occasion a saving in Paris alone of more than 10,000 francs 

 annually, and therefore deserves to be more extensively known. 

 This cement is generally employed to close the joints of the stones 

 with which most terraces are covered, &c. &c. What takes place 

 in this operation, it is easy to see — the iron filings with which the 

 joints are filled up, occupying a larger space in proportion as they 

 become oxidized, the oxidation being facilitated by the action of 

 the acid with which they are impregnated, the joints become exactly 

 closed. — Journal de Pharmacie — Aodt. 



