Elsewhere, the process of manufacture often vitiates the air, as the "blow-over" in bottle shops. "In some factories, at times the air is so full of this floating glass that the hair is whitened by merely passing through the room. It sticks to the perspiration on the face and arms of the boys and men and becomes a source of considerable irritation. Getting into the eyes it is especially troublesome" (l. c., p. 66). Something similar occurs in etching glass by a sand-blast. Unless a hood and exhaust are provided, a pressure of from fifty to ninety pounds scatters fine sand and glass dust through the air and is breathed in by the operator (l. c., p. 440). Even worse, however, is the acid etching, as the fumes of hydrochloric acid cause severe irritation to the throat and lungs (l. c., p. 442). Even when there is no such irritant in the air as just mentioned, extreme differences in temperature between the work-room and the outside, or between various parts of the shop, may be a source of serious danger to health. In the glass industry, many persons have to work in temperatures ranging from ninety to one hundred and forty degrees, and as high as fifty degrees above the outside air (l. c., p. 75). Industries where an artificial humidity is required, such as silk, cotton and flax spinning, are likely to induce rheumatism, pleurisy, etc. After working ten hours in a room filled with live steam to prevent breaking of threads, to pass into a New England blizzard is apt to produce serious results. The boys in bottle-making shops are obliged to pass continually from a temperature of 140 degrees at the "glory-hole" to one of 90 degrees or less in other parts (l. c., pp. 49ff.). And even if conditions of atmosphere and ventilation are good, the mere fact of continuing work for thirteen hours seven days a week tells seriously upon the physical endurance of the strongest.[68] When night work is required in addition to the day's labor, as in the glass industry, the consequences are likely to be worse, especially where children are concerned.[69] Night work frequently means a presence in the factory of at least twenty hours out of the twenty-four. "During the course of the investigation there were found two cases of recent death, both children, which could be directly attributed to exhaustion due to double-shift work in the furnace room" (l. c., p. 122).