POWDEKS WITH SODIUM NITKATE. 515 



9. On the whole, blasting powder offers hardly any other 

 advantage than its low price, due to the diminution in the 

 weight of nitre. It would certainly be preferable to employ a 

 less weight of ordinary powder, which would realise the same 

 economy. Moreover, the daily increasing use of dynamite tends 

 to limit the consumption of blasting powder. 



10. POWDERS WITH SODIUM NITRATE BASE. 



1. Sodium nitrate lends itself as well as potassium nitrate to 

 the manufacture of powders ; it has been employed on a large 

 scale in the Isthmus of Suez works, and offers a marked 

 economy. It has also been employed in the mines of Freyberg 

 and Wetzlar. 



Unfortunately this salt is very hygroscopic, and the keeping 

 of the powders into the composition of which it enters needs 

 special precautions. 



2. Thermal theories increase the interest there may be in 

 overcoming these difficulties by showing that the powder with 

 sodium nitrate base develops a greater pressure, weight for 

 weight, than powder with potassium nitrate base, and that it 

 can effect a greater work. 



3. Take, in fact, a composition equal to that of powder, 

 such as 



Saltpetre 75 



Sulphur 10 



Charcoal 15 



It would correspond by weight to the following proportions : 



Sodium nitrate 71*8 



Sulphur 11-3 



Charcoal 16'9 



4. Supposing the chemical reactions to be exactly the same, 

 the heat liberated and the gaseous volume would also remain 

 nearly the same at equal equivalents (p. 4). But at equal 

 weights there would be, on the contrary, an eighth more heat, 

 or for 1 kgm. 782 Cal. from the calculation (or 818 Cal. for 

 carbon derived from wood charcoal), there would further be a 

 volume of gas equal to 338 litres. 



The resultant force would retain the same expression, but 

 it would be increased by about an eighth for a given density of 

 charge. Such are the results indicated by theory. But up to the 

 present no experiment has been made to study the true re- 

 actions. 



5. In general, powders with sodium base will develop stronger 

 pressures and a greater quantity of heat, that is of work, than 

 the same weight of powders with potassium base and of equiva- 



composition. Indeed, experiment proves that the substitu- 



2 L 2 



