76 



SCIENTIFIC NEWS. 



[July 27, 1888. 



War, but he passed them without modification, after 

 considering them for nine months. Work was at once 

 commenced, but an injunction was obtained against the 

 Company, which delayed progress for another six 

 months. In spite of these difficulties, however, on June 

 13th, the swing-bridge was swung round from the open 

 to the closed position, thus completing the bridge three 

 days in advance of the stipulated time. 



The trusses and swing-bridge are carried upon five 

 piers of masonry, but much trouble was experienced in 

 obtaining a solid foundation. 



The entire length of the bridge proper, exclusive of 

 approaches, is 800 feet. It comprises two shore spans, 

 each 150 feet long, covered by fixed trusses, and two 

 draw spans, closed by the great draw-bridge. The draw- 

 bridge is said to be the largest now in existence, its total 

 length is 500 feet. When open there is a clear water- 

 way 208 feet wide on each side of the central pier. 



The draw span was put together in four weeks, and 

 the machinery was installed in another fortnight. The 

 draw contains 656 tons, and each of the approaches 85 

 tons of metal. The approaches have yet to be made, 

 but it is anticipated that by the end of August trains will 

 be running across the bridge. 



POISONS IN THE WORKSHOP. 



(Continued from page 14.) 



OF all the dangerous materials employed in the arts 

 and manufactures, perhaps the one most to be 

 dreaded is lead. This we say not by reason of the 

 violence of the symptoms which it produces if introduced 

 into the human body, but on account of the insidious 

 nature of its attacks, and of the great number of manu- 

 facturing operations in which it plays a part. 



We are not aware that the lead-miner is liable to 

 diseases more and other than those which in general befall 

 persons employed underground. Nor are the men em- 

 ployed in smelting and refining lead, in the manufacture 

 of sheet-lead and leaden piping, of shot, and of the chief 

 commercial alloys of this metal, such as plumbers' solder 

 and type-metal, very frequent sufferers from lead- 

 poisoning. The reason for their comparative immunity 

 is that they have to deal with the noxious substance in a 

 solid, insoluble, and non-volatile state. Their work, too, 

 is very generally performed in the open-air or in open 

 sheds. But it is when lead is made the subject of 

 chemical operations that its hurtful character is most 

 felt. 



Foremost among the dangerous preparations of lead 

 stands the well-known paint white lead, a carbonate, or 

 rather a mixed carbonate and hydrate of lead. Into the 

 manufacture of this pigment there is no occasion for us 

 to enter. But it is produced and consumed in vast 

 quantities, and often occasions in the workmen who 

 make or who use it the most characteristic and dis- 

 tressing symptoms of lead-poisoning. The victim ex- 

 periences severe cholic, "wrist-drop" sets in — that is, the 

 hands hang down uselessly at the wrist or can be 

 raised only with great difficulty — a general tremor is 

 experienced in all the limbs, and sometimes complete 

 paralysis comes on. The cause of the mischief is re- 

 vealed by a blue-black line in the gums below the roots 

 of the teeth. 



Much of the ill-effects of the white lead manufacture 



may be avoided by due care on the part of the men. The 



" chief precautions are strict attention to personal clean- 



liness, so that none of the dust of the white lead may 

 remain on the skin. No food or drink should ever be 

 partaken of or be allowed to remain in any of the work- 

 rooms, and "sulphuric acid lemonade" — that is, 

 sweetened water with a few drops of pure sulphuric acid 

 to the glass, enough to communicate a pleasant tartness 

 without setting the teeth on an edge — should be used as 

 the ordinary drink. It is not pleasant having to admit 

 that in some cases where white lead manufacturers have 

 provided protective appliances, such as hot baths, a room 

 where such of the men as live at a distance may take 

 their meals away from the poisonous substance, all such 

 precautions are neglected, if not positively refused. But 

 the habitual use of white lead is as dangerous as its 

 manufacture. The house-painter is constantly using 

 white lead, not merely alone, but as an ingredient in 

 most compound colours. The turpentine with which so 

 many oil colours are mixed is highly volatile, and carries 

 particles of white lead, too minute to be visible, into the 

 mouth and lungs. Hence the painter — it is a painful 

 deficiency that in the English language one and the 

 same term is applicable to the artist and to the man 

 who coats window-frames, doors, and walls with colours 

 — is open to cholic and paralysis just like those employed 

 in white lead works. 



In the hopes of escaping this evil, a variety of substances 

 have been proposed as substitutes for white lead, but none 

 of them appear to suit the demands of the trade to an equal 

 extent. Zinc white has, indeed, been used in practice to a 

 very considerable extent, and possesses the great ad- 

 vantage of not becoming discoloured if exposed to sul- 

 phuretted hydrogen, coal-gas, etc. Another fraudulent 

 use of white lead has been an unsuspected cause of 

 poisoning. Everyone in these days knows what is 

 meant by " weighting" or " loading " silks — a variety of 

 practices by which a pound of genuine silk is converted 

 into from 18 to perhaps 40 ozs. of a something which can, 

 at any rate, be sold as silk. Now, in the case of white 

 sewing silk this loading is chiefly effected by means of 

 white lead, which is deposited on or attached to the fibre. 

 Hence sempstresses, or ladies who often make use of 

 white sewing silk, especially if they have the bad habit 

 of biting off the ends of the thread, or trimming it with 

 the lips before threading the needle, have been known to 

 suffer from lead-poisoning. 



Girls employed in artificial flower-making, especially 

 in the case of wax flowers, are often similarly attacked, 

 as very many of the pigments used contain white lead, 

 alone or in admixture. 



The manufacture of rubber articles is also not un- 

 attended with danger, as compounds of lead are not 

 unfrequently employed for giving weight. Lead meets 

 us further in the paper-hanging trade. Perhaps it may 

 have been somewhat overlooked because the attention of 

 physicians, analysts, and of the general public has been 

 mainly turned to the arsenical compounds still, un- 

 fortunately, in so common use. But the lead is also 

 there, and does its share of mischief. 



Red lead is much less poisonous than white lead. It 

 is less soluble in the secretions of the body, much denser, 

 and hence less liable to form dust, and its use is much 

 less general. 



Chrome-yellow,thechromatesof lead of various shades, 

 will be discussed among the compounds of chromium, of 

 which we shall speak below. 



Tin and zinc are both more evidently poisonous than 

 lead. Yet their employment in the arts presents little 



