_It must not be thawed by a fire_, but by hot water in an apparatus like a common glue-pot, the dynamite being in the inner vessel and hot (not boiling) water in the outer. Eissler states that there is but one safe way of thawing it, which is to keep it in a kitchen or other room at summer heat, and away from the fire, until it is soft. It is then ready for use. =Precautions.=--Never attempt to thaw frozen dynamite by _roasting_, _toasting_, or _baking_ it. Never put it in heated vessels, or in boilers, or before fires or heated metals. _It must not be thawed or heated rapidly._ Never put a cap into a charge or primer until you are ready to use it. After it is made never let a primer leave your hands until it is in the hole. Keep the caps away from the dynamite. Never let them come near each other except when used. Never allow smoking or other fire near the powder or explosive, as it burns rapidly, and especially when loose, and may fire caps incautiously left near by, and thus bring on an explosion. Never use a metallic rammer. Do not get nitro-glycerine on your fingers. It will be absorbed by the skin and give you a headache. Invariably prepare your primer at a distance from your explosive. RACK-A-ROCK. This powerful explosive, composed of a solid and a liquid ingredient, entirely inexplosive when separate, but easily and quickly combined, seems to present undoubted advantages for use in the military service. The solid is potassium chlorate, and the liquid is either "dead oil," or dead oil and bisulphide of carbon in equal volumes, or bisulphide of carbon with 3 per cent of carbon added, or mono-nitro-benzine. General Abbot considered the following the best: Potassium chlorate, 79 parts; mono-nitro-benzine, 21 parts. The potassium chlorate is put up in the form of a cartridge enclosed in a bag made of cotton or other suitable material. In preparing the charge for use the cartridges are placed in a wire frame, which is suspended from a spring-balance, and dipped in the liquid until a proportion of 3 to 4½ parts of solid to 1 part of liquid is shown by the balance; this requires from 3 to 6 seconds. Or, place the cartridges in a pan containing cells (each cartridge having a corresponding cell and cup) and then pour in each cell its cupful of liquid. As soon as it has all been absorbed remove the cartridges and in ten minutes they are ready for use. If the cartridges be kept, they appear to tend to increased sensibility to friction or percussion. GUNCOTTON.