738 Transactions of tee American Institute. 



eoustructed on the principle first fully illustrated by Thomas Ewbank 

 of New York, which was many years after applied by Gifiard of 

 France, in the coustructiou of his injector, viz: that the rapid cur- 

 rent of a fluid draws in the same direction any other fluid in con- 

 tact with it. Mr. Fletcher places in the flue a straight tube in 

 direction of the current of air, and in connection with it a tulje 

 bent, so as to face the current; both are connected with a column 

 of ether, and the difierence in the pressure in each will be indica- 

 ted by the height of the ether in the graduated column, which 

 measures the force of the current in the flue. The same instrument, 

 with a slight modification, may be nsed as a wind gauge. 



PYEOTECHNICAL. 



M. Pool makes a fast or slow burning powder by substituting 

 common glue for charcoal in the ordinary process. He soaks his 

 glue or gelatine in cold water, then heats it with nitric acid, and 

 after evaporating the solution to dryness, he re-dissolves it in hot 

 water, and adds sufficient carbonate of baryta {barmant) to neutral- 

 ize the nitric acid. The solution is evaporated again, and two parts 

 of sulphur and six of nitrate of potash {kahnan'i) are added as the 

 evaporation proceeds. By varying this process, he also makes a 

 slow burning powder. His compound for producing red fire con- 

 sists of five parts of glue, treated as above described, with seven 

 parts of saltpeter and five of chlorate of potash {Jcalemedeet); to 

 these is added a mixture of three parts of nitrate of strontia 

 (stronmeneat), with one of charcoal. The Mechanics^ Magazine says 

 the chief merit of this compound is its non-liability to spontaneous 

 ignition. 



PROTECTION OF STONE BUILDINGS. 



Mr. J. Spiller read a paper at the last meeting of the British 

 Association, in which he showed that the sulphurous and sulphuric 

 acids in the atmosphere, and resulting from the burning of coal 

 fuel — the best of which, as well as the^coke, must contain at least 

 one per cent of sulphur — acts in a very destructive manner upon 

 dolomite and the numerous class of limestones commonly employed 

 in the public buildings. As a remedy for the decay of stone, ho 

 proposes to apply to its cleaned surface an aqueous solution of the 

 superphosphate of lime, which should not contain any appreciable 

 amount of sulphuric acid; the specific gravity of the solution when 

 ready for use should be about 1. 1. One gallon will cover about 

 three hundred superficial feet, when two coatings are applied to 



