Hexa-nitrate, C_{12}H_{14}O_{4}(NO_{3})_{6},[1] gun cotton. In the formation of this body, nitric acid of sp. gr. 1·5, and sulphuric acid of sp. gr. 1·84 are mixed, in varying proportions, about 3 of nitric to 1 of sulphuric (sometimes this proportion is reversed), and cotton is immersed in this at a temperature not exceeding 10° C. (50° F.) for 24 hours: 100 parts of cellulose yield about 175 of cellulose nitrate. The hexa-nitrate so prepared is insoluble in alcohol, ether, or mixtures of both, in glacial acetic acid or in methyl alcohol. Acetone dissolves it very slowly. This is the most explosive gun-cotton. It ignites at 160°–170° C. (320°–338° F.). According to Eder the mixtures of nitre and sulphuric acid do not give this nitrate. Ordinary gun cotton may contain as much as 12 per cent. of nitrates soluble in ether-alcohol. The hexa-nitrate seems to be the only one quite insoluble in ether-alcohol. [Footnote 1: To represent the series of cellulose nitrates so as to avoid fractional proportions, the ordinary empirical formula is doubled and the nomenclature has reference to this double molecule.] Penta-nitrate, C_{12}H_{15}O_{5}(NO_{3})_{5}. This composition has been very commonly ascribed to gun-cotton. It is difficult, if not impossible, to prepare it in a state of purity by the direct action of the acid on cellulose. The best method is the one devised by Eder, making use of the property discovered by de Vrij, that gun-cotton (hexa-nitrate) dissolves in nitric acid at about 80°–90° C. (176°–194° F.) and is precipitated, as the pentanitrate, by concentrated sulphuric acid after cooling to 0° C. (32° F.); after mixing with a larger volume of water, and washing the precipitate with water and then with alcohol, it is dissolved in ether-alcohol, and again precipitated with water, when it is obtained pure. This nitrate is insoluble in alcohol, but dissolves readily {10} in ether-alcohol, and slightly in acetic acid. Strong potash solution converts this nitrate into the di-nitrate, C_{12}H_{18}O_{8} (NO_{3})_{2}. The tetra- and tri-nitrates (collodion pyroxyline) are generally formed together when cellulose is treated with a more dilute nitric acid, and at a higher temperature, and for a much shorter time (13 to 20 minutes), than in the formation of the hexa-nitrate. It is not possible to separate them, as they are soluble to the same extent in ether-alcohol, acetic ether, acetic acid or wood spirit. On treatment with concentrated nitric and sulphuric acids, both the tri-and tetra-nitrates are converted into penta-nitrate and hexa-nitrate. Potash and ammonia convert them into di-nitrate.