These points secured, viz: purity and strength of materials, i. e., glycerin free from sugar, fatty acid, saline impurities, and a mixture of Sulphuric Acid with Nitric Acid in due proportion, of due percentage of the respective acids, and not more water therein, nor in the glycerin, at one time of making, than another; the next point to command will be, that in combining the glycerin with the acids, when considerable heat is evolved, the heat thus evolved shall be absorbed rapidly, so as never under any circumstances whatever, to exceed a certain temperature. Sobrero names 32°F; otherwise, according to my experience, very differing nitro-glycerin will result from variation of temperature whilst mixing. Such products may be fatal to the miner, although only affecting the manufacturer in a pecuniary sense. I am led to emphasize these remarks from the fact that prospectuses have been issued to tempt contractors to buy apparatus in the one case, and offering to manufacture on the side of a railroad cutting, if required, in another case, by parties who have no experience in the manufacture, and who start in their new avocation, by deriding the care, outlay and precautions that their competitors have deemed it necessary to make, in order to secure a uniform, certain, and, for mining purposes, perfectly safe explosive; for as the product is to be handed over to the uneducated miner, who cannot estimate the risk he is subjected to even if such a course occurred to him, it does seem to me just and proper, that the controlling engineer, the intelligent contractor, and especially the operating miner who is to handle this explosive, should be advised, that under the term Nitro-Glycerin, very different substances, both as regards explosive force, and liability to spontaneous explosion, do result, unless extraordinary precautions are adopted in the selection of the crude materials, as well as securing uniformly low temperature throughout the process of making. Unless this be done, decomposition sets in and is indicated by the emanation of fumes, by the deepening of the light lemon tint to an orange yellow, and at this point, the miner should decline using it, and require the manufacturer to take his place, and the risks contingent on using it.