FIREPROOFING AND ZINC WATER.
Concerning the zinc water method of making wood fireproof, mentioned in FIRE AND WATER last week, N. Utzer of Pittsburgh states that about eight years ago, after many years of chemical research, he discovered that wood could be made absolutely non-combustible if treated in the following way: Common zinc was dissolved under a pressure of two atmospheres in hydrochloric acid ; this process took place in iron stills coated upon the inside with a thick coat of asbestos cloth. The solution was treated with lime to remove all excess of acid, and then varied proportions of borax in watery solution added. The beams or boards to be treated were first dried in a kiln and then placed in an iron frame provided with screws on the principle of a monkey wrench, so that the four sides of the iron frame could be screwed tight upon the surface of the wood. Then one end of the wood was placed in the above zinc solution and the other end fitted to a suction pump and subjected to a strong suction. Through drying in the kiln all of the moisture had been expelled out of the cells of the wood. Under a microscope a section of the wood presented an appearance similar to a honey-comb. Naturally, as soon as suction was produced the zinc liquor ascended through the wood as readily as the sap penetrates upon a warm spring day. It required about ten minutes to saturate a beam twelve inches square and sixteen feet long. At the end of ten minutes the beam was taken out of the frame and placed aside to dry. Chloride of zinc itself dries rapidly ; that is, the water of solution evaporates, leaving the dry salt. It generally took two days for a beam as above to dry completely. By this treatment the physical appearance and structure of the wood had changed most remarkably, common pine wood—I always used pine—had acquired the hardness of oak and the suppleness of hickory. But the most remarkable change was in its behavior towards fire. Placed in a glowing fire a piece of wood treated as above would not burn, did not even commence to glow, but merely “oxidized” away—if such an unchemical expression may be used. A coating of coke or charcoal would slowly form, covered with an incrustation of chloride of zinc, which gradually, through the agency of the heal, changed into yellow oxide of zinc. It was only after this layer was removed that the action of the fire proceeded further and formed a second layer.