398 THE POPULAR SCIENCE MONTHLY 



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 inflam- 

 mable nature of the wood employed in the construction of the theater 

 and for the decorations and scenery but also on account of the inflam- 

 mability 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, recom- 

 mended a mixture of alum and green vitriol whereas, in the Diction- 

 naire 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 effec- 

 tive 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, there- 

 fore, 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 fire- 

 proofing 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- 



