1638 when Nikolas Sabattini published a remarkable paper in which he discussed the need of reform in the administration and construction of the theaters in Italy and pointed out the danger, which is always present, of fire breaking out on the stage, not only owing to the inflammable nature of the wood employed in the construction of the theater and for the decorations and scenery but also on account of the inflammability of the cotton material used in the scenery and for the dresses of the players.
He recommends, as a safeguard, that the color used in painting the theater and scenery should be mixed with clay and gypsum but says nothing about the fireproofing of the dresses.
At a considerably later date—in 1735—Wild suggested a mixture of alum, borax and sulphuric acid for the same purpose and, in 1710, Fagot, in a paper read before the Academy in Stockholm, recommended a mixture of alum and green vitriol whereas, in the Dictionnaire de l'Industrie published in the year 1786, there is a paragraph in which it is stated that a mixture of alum, green vitriol and salt is effective in making wood and other material fireproof.
After the disastrous fire in Munich on the fourteenth of January, 1823, which completely destroyed the Hof and National Theater, a large number of experiments were made with the result that the wood used in the construction of the roof and other parts of the new theater, was painted with several coats of sodium silicate and chalk.
A coating of this kind lasts for many years and, although it does not render the wood absolutely non-inflammable, it has at least this value that the incipient fire, which, as a rule, begins in quite a small way, meets with resistance at the outset, progresses but slowly and is easily extinguished.
At a somewhat later date, it was discovered that wood saturated with other salts such as, for example, copper sulphate or ammonium phosphate, acquires the property of resisting flame, but of all the salts, zinc chloride seems to be the most efficient for this purpose.
In the first place, zinc chloride has great affinity for, and, therefore, attaches itself readily to, woody fiber, and fibers of all kinds and material saturated with a solution of this salt and then dried are practically non-inflammable. This salt has also this valuable property that it is a powerful antiseptic and therefore very suitable for fireproofing the wood used in the construction of hospitals and other public institutions of a similar nature.
But I do not propose to address you this afternoon at any length on the subject of the fireproofing of wood and other building materials, a subject on which I have made comparatively few experiments and of which I, therefore, have little practical knowledge.
What I wish to discuss, and I hope that the subject will prove in-