28 REPORT—1863. 
b. Nitric acid.—The nitric acid employed must be in the highest possible 
degree of concentration ; and here the remark should be made, that an impurity 
of hyponitric acid imparted to the acid by concentration, and which is difficult 
to climinate, does not prejudice the acid for this special application. 
c. Sulphuric acid.—The ordinary commercial sulphuric acid of spec. grav. 
1:84 answers perfectly. 
d. Mixture of the acids——This consists of one part by weight of nitric acid, 
and three parts (weight) sulphuric acid,—assuming the nitric acid employed to 
possess an average specific gravity of 1-485. If, however, the specific gravity 
should differ from the above, then cognizance of the amount of anhydrous 
acid supplies the data necessary for regulating the mixture. 
The mixture is effected by means of an apparatus represented by fig. 1.* 
The vessel C is filled with the predetermined quantity (equivalent to the re- 
quired weight) of nitric acid; Band D with sulphuric acid. This being done, 
the acids from the three vessels are allowed to run very slowly into F, in which 
is an agitator T, set in motion by the handle L. As soon as a portion of the 
two acids has been mingled in this manner, the mixture is allowed to run from 
F to G, and the operation resumed as before. 
The reservoir G being completely filled, its contents must be set aside in 
closed vessels. It is advantageous to preserve the mixed acids a considerable 
time in the above vessels ; in no case must the mixture be used until it has 
become quite cold. 
e. Process of steeping—Cotton-wool ordinarily absorbs about 6 per cent. 
of atmospheric moisture, which must be dissipated in a drying-room heated 
to 95° F. previous to dipping the cotton. 
Steeping is effected in an apparatus represented by figs. 2, 2a, and 2b. The 
apparatus, during the process, is kept cool by a constant change of cold water 
poured into the vessel F. The chamber A contains a store of acid, B sixty 
pounds of the acid mixture, D represents the vessel in which the cotton is 
stored after dipping is accomplished. Two skeins (about 3 ounces) of dried 
cotton are dipped at one operation in the mixture contained in B, the spatula 
G being used to effect, by pressure, complete incorporation between acid and 
cotton ; in the next place, the cotton is to be removed from the bath, laid 
upon the rack C, and pressed to such extent that the amount of mixed acids 
left absorbed by the cotton. be in the ratio of 103 lbs. of the former to 1 1b. 
of the latter. The cotton being now lifted into the vessel D, this is to be 
filled with mixed acids, and the portion of acid absorbed made good by 
means of the tared spoon E, in such manner that the surface in B may 
always maintain the same level for every additional portion of cotton dipped. 
The vessel D filled in the manner prescribed, is at length set aside, the 
due proportion of its contents being regulated, if necessary: the regulation 
is easily accomplished after a little practice, but it is seldom requisite. The 
cotton is next compressed by the handle H in such manner that it is wholly 
covered by acid, to the further action of which it is left exposed for the space 
of forty-eight hours; it must be cooled during that exposure, thus guarding 
against the violent action of the acids resulting in decomposition. 
f. Removal of acid from the gun-cotton.—This is performed by means of a 
centrifugal machine, the drum of which is of copper, a material which 
lasts a considerable time; after this manipulation, there still remain 3 lbs. 
of acid in the gun-cotton manufactured from 1 lb. of ordinary cotton. This 
must be got rid of by rapid water affusion applied in some convenient 
manner, 
* This refers to a drawing exhibited at the time. Sec Plate III. 
