Both the accurate information of the pyrotechnist, and the handicap under which he worked, due to ignorance of certain chemical facts, are well illustrated in the summing up of one writer concerning colors in fireworks.
This expert declares that saltpeter, sulphur, charcoal, and iron are almost the only materials of which use is made in firework manufacture. Different combinations of these vary both the general effects and the particular color of the fires produced. These colors show a series of finely graded nuances from red to white. Sulphur, when it predominates, gives a blue flame, while iron produces sparks of special brilliancy. Many experiments have been made in an effort to discover other colors, but none has been successful. The materials best suited to such purposes, by which, when melted, the effects are naturally produced, such as zinc, copper, and other metals, fail to produce the desired effects when they are mingled with sulphur and saltpeter, since the more powerful fire of these substances destroys the phlogistic metallic content, which is the color source.
The French writer continues with the statement that there is, nevertheless, a composition producing a beautiful green flame. This consists of a half ounce of salammoniac and a half ounce of verdigris, which has been dissolved in a glass of vinegar. Bits of paper or of linen, or wood shavings, are soaked in this liquid, and show a green light in burning. Unfortunately, this composition is unable to resist the fire of sulphur and saltpeter, so that it is unavailable for use in the making of fireworks.
Another French authority gives a careful study of the various chemical substances employed in pyrotechny. His conclusions, also, are interesting by their revelations of both his knowledge and his lack of it.