USE OF ZINCED OR GALVANIZED IRON.

The Report of the State Board of Health of Massachusetts, for the year 1871, contains a paper upon "Poisoning by LeadPipe," which is confirmatory of the now well-recognized fact, as illustrated in the following paragraph (p. 40):-" From the evidence presented in the preceding pages, it seems reasonable to believe that the use of lead-pipe for the conveyance of drinking-water is always attended with a certain degree of danger, because such water always contains lead; and that this danger varies in degree with the character of the water conveyed and the susceptibility to lead poison of those who drink it."

With the view of obviating the dangers arising from the use of lead-pipe, different methods and materials have been suggested from time to time. In this way, zinced (or what is termed commonly galvanized) iron has come into use, and at the present time is extensively employed, both in this country and in Europe, for the purpose of roofing material, gutters and conductors, reservoirs, water-conduits, bathingtubs, cooking utensils, etc.

The object of the present paper is to determine, if possible, whether or not the employment of this material for the storage and conduction of drinking-water is attended with danger of zinc poisoning, as has been re-affirmed recently.*

The various modes of protecting iron, with the exception of mere superficial coverings, have all been of the electro-chemical class, and have been derived, in various ways, from suggestions deduced from the experiments and observations of Sir Humphry Davy,† for the protection of the copper sheathing

Boston Journal of Chemistry, Vol. V., 1871, passim.

† Phil. Trans., Vol. CXIV., 1824, and Phil. Mag., 1st Ser. Vols. LXIV. and LXV.

of vessels. In his paper on this subject, the author developed the principle of counteracting chemical by electrical forces. Subsequently his idea was adapted to particular

cases.

He stated that it follows from the principles which he developed, that cast or wrought iron may be preserved from chemical action by suitable protectors of zinc or tin. Prof. Edmund Davy was the first to publish a series of experi ments which he undertook with the view of determining this protective power of zinc, which he employed in simple contact and in massive form. Shortly after the publication of the results of these experiments by Prof. Davy, M. Sorel, a French engineer, obtained a patent for the protection of iron against rust by coating its surface with fluid zinc, and, with this patent, the first manufactories of zinced or galvanized iron were established in London, under the style of the "British Galvanization of Metals Company," and the "Zinced or Galvanized Iron Company." Prof. E. Davy, however, claiming priority of discovery, stated that he had employed this method of zincing iron so far back as 1834, yet we have no other record of such experience than his simple statement. Without knowledge of the principle, however, Madame Leroi de Jancourt was granted a patent on the 26th of September, 1791, for preserving metals from rust by covering them with an alloy of zinc, bismuth and tin.

Zinced or galvanized iron is prepared by dipping the iron, previously well cleaned by means of dilute acid, into melted zinc. By this process, the iron becomes superficially combined with the zinc, and there is furnished, as claimed by the first manufacturers, a material which is adapted for use as water-pipes, reservoirs, etc., is durable, cheap, and is unattended with danger to the human system in the way that lead is when employed for similar purposes.

In order to discuss connectedly and to the best advantage the subject which we have in view, it has been deemed advisable to consider it under the following heads, viz. :—

1. Is the zinc of galvanized iron acted upon by water, and what are the products of such action?

*Report of the British Association for 1835.

2. Do these products exert a poisonous action upon the human system?

1. The action of water upon zinc has been recognized for a long time. In the year 1778, M. de la Falie, a French physician and chemist, in place of vessels of iron, copper, etc., then employed for culinary purposes, proposed the use of iron vessels lined with zinc, principally upon three grounds; namely, because, in his opinion, the zinc would not be dangerous; such vessels would not be very expensive, and they would be more durable.* A subsequent report to the French Academy of Sciences disapproved of the use of these vessels, on the ground that the zinc is removed and endangers the health. Discoveries of new sources of supply of the metal and of the means of rendering it more useful in the arts, led to the revival of its employment, by MM. Douey and Montagnac, in the manufacture of culinary articles, roofing materials, reservoirs, water-conduits, etc. The first petitions of these gentlemen to the proper authorities having been reported upon unfavorably, by MM. Thenard and GayLussac, they made another petition which led to a series of experiments by MM. Vauquelin and Deyeux,‡ under the authority of the Academy of Sciences. In their report they state that zinc is acted upon by water, the weakest vegetable acids and butter; that water, allowed to stand in zinc vessels, was partly decomposed and a white oxide was produced, while the water covering the oxide had a metallic taste.

M. Schaufele § made a series of careful experiments, the results of which were confirmed later by distinguished chemists, notably by Payen and Chevallier, with the view of determining the action of various substances upon zinc. He found that common water, allowed to stand in a galvanized iron vessel, presented traces, very slight indeed, of zinc at the expiration of thirteen hours; that common water, placed in pure zinc vessels, gave no indication of the presence of

* Annales de Chimie, t. 86, p. 51. 1813.

Jour. de Med. de Corvisart, t. 36, p. 225.

Annales de Chimie, t. 86, p. 51. 1813.

§ Jour. de Chim. Méd., t. iv., p. 663, 1848, and Tardieu, Dict. d'Hyg. Publique, t. 3, p. 708. 1854.

Tardieu, loc. cit.

zinc; that distilled water showed traces of zinc, in five hours, both in pure zinc and galvanized iron vessels.

Similar results have been reported by numerous reliable observers. Prof. Wm. Ripley Nichols, of the Massachusetts Institute of Technology, remarked to the writer that he always expects to find zinc in water which passes through galvanized iron pipes, and, in a written communication, he stated that a specimen of water drawn from the pipes, which have been in use in the Institute for eight or nine years, contained a small amount of zinc in suspension, and in solution an amount equal to 0.062 grain to the gallon. The water had remained undisturbed in the pipes for about thirty-six hours.

Another specimen of water was examined by Prof. Nichols, at the request of the writer. It was spring-water which had passed through between forty and fifty feet of zinced pipe, from which no water was drawn previously for about twentyfour hours. The analysis gave rise to a suspicion of drainage contamination, and detected a trace of zinc in suspension and 0.843 grain to the gallon in solution.

This subject of the action of water on zinc has been most ably treated by Robert Mallet, who drew up a series of papers showing the results of experiments made by himself, with the view of determining the best protector for iron against corrosion by air and water. Among the conclusions derived from his prolonged and carefully conducted experiments, the following may be quoted in proof of the affirmative. of our question :

"OF CAST-IRON IN SIMPLE CONTACT WITH ZINC, IMMERSED IN FRESH WATER. "If cast-iron be perfectly free from any initial stains of rust and quite homogeneous in texture, it is electro-chemically preserved by an equal surface of pure zinc for an indefinite period, during which the zinc is oxidated, and forms mammillary concretions on the iron; after which the protective power of the zinc is greatly diminished, and, at this stage, the contact of any substance, even a neutral one,-such as glass,-with the iron, is sufficient to originate oxidation upon it.

"If cast-iron, having a polished surface, is suffered to contract any coating of rust, although the surface be afterwards perfectly polished to the eye, yet zinc, in simple contact, has lost nearly the whole of its power of protection; the zinc and iron both oxidate from the moment of immersion.

* Report of the British Association, Vols. VII. and IX., for 1838 and 1840.