286 COMPOUNDS DERIVED FROM NITBIC ACID. 



6. Nitrostarch (Xyloidin). 



1. This body answers to the formula in the following equa- 

 tion : 



C 6 H 10 6 + HNO S = C 6 H 8 4 (HN0 3 ) + H 2 0, 



or rather, to a multiple of this formula, if we admit that starch 

 is itself a condensed body, derived from several molecules of 

 glucose 



Since the value of n is not definitely known as yet, it is con- 

 venient, for the sake of simplicity, to reduce the data to a value 

 of n = 1. 



2. Nitrostarch was prepared from a mixture of dry starch and 

 nitric acid, sp. gr. 1*5. It was found that the reaction 



C 6 H 10 5 + HN0 3 = C 6 H 8 4 (HN0 3 ) + H 2 0, 



gives off 12 *4 Cal, the nitrostarch separating out in a solid 

 form. 



This is almost the same value for each equivalent of fixed 

 acid as we get for gun-cotton. 



It will be noticed that this value is double that got for nitric 

 ether and nitroglycerin, while it is only a third of the heat 

 disengaged in the formation of nitrobenzene. Gun-cotton and 

 xyloidin behave as substances intermediate between nitro-com- 

 pounds and normal nitric ethers ; they also resist alkalis far 

 better than nitric ethers. 



3. The heat of formation of nitrostarch from its elements may 

 be calculated, if we admit, with M. Eechenberg, that the heat 

 of total combustion of starch is equal to + 726 Cal. ; its heat of 

 formation will be equal then to 183 Cal We shall find, then, 

 that 



C 6 + H 9 + N + 7 gives off + 183 + 41-6 + 12-4 - 69 = 



+ 168 Cal. for 207 grms., 

 or, for 1 grm., 812 cal. 



4. The heat of decomposition could only be calculated if the 

 products of this decomposition were given ; but they have not 

 as yet been studied, and the quantity of oxygen contained in 

 the compound is far from being sufficient for its complete com- 

 bustion. 



5. The heat of total combustion is equal to 706'5 Cal. for 207 

 grms., or, for 1 grm., 3413 cal. 



7. Pernitro-cellulose, or Gun-cotton. 



1. This substance results from the action of nitric acid upon 

 cellulose, the latter being taken under the particular form 

 of cotton. Nitric acid replaces the elements of water of the 

 cellulose, without altering in any way its physical appearance. 



