Chapter 6

On the 8th of June. 1874, Tresca presented to the French Academy some considerations respecting the distribution of heat in forging a bar of platinum, and stated the principal reasons which rendered that metal especially suitable for the purpose. He subsequently experimented, in a similar way, with other metals, and finally adopted Senarmont's method for the study of conductibility. A steel or copper bar was carefully polished on its lateral faces, and the polished portion covered with a thin coat of wax. The bar thus prepared was placed under a ram, of known weight, P, which was raised to a height, H, where it was automatically released so as to expend upon the bar the whole quantity of work _T=PH,_ between the two equal faces of the ram and the anvil. A single shock sufficed to melt the wax upon a certain zone and thus to limit, with great sharpness, the part of the lateral faces which had been raised during the shock to the temperature of melting wax. Generally the zone of fusion imitates the area comprised between the two branches of an equilateral hyperbola, but the fall can be so graduated as to restrict this zone, which then takes other forms, somewhat different, but always symmetrical. If A is the area of this zone, b the breadth of the bar, d the density of the metal, c its capacity for heat, and t-t0 the excess of the melting temperature of wax over the surrounding temperature, it is evident that, if we consider A as the base of a horizontal prism which is raised to the temperature t, the calorific effect may be expressed by:

Ab x d x C(t-t0);

and on multiplying this quantity of heat by 425 we find, for the value of its equivalent in work,

T' = 425 AbdC(t-t0).

On comparing T' to T we may consider the experiment as a mechanical operation, having a minimum of:

T'/T = (425/PH)AbdC(t-t0).

After giving diagrams and tables to illustrate the geometrical disposition of the areas of fusion, Tresca feels justified in concluding that the development of heat depends upon the form of the faces and the intensity of the shock; that the points of greatest heat correspond to the points of greatest flow of the metal, and that this flow is really the mechanical phenomenon which gives rise to the calorific phenomenon; that for action sufficiently energetic and for bars of sufficient dimensions, about 0.8 of the labor expended on the blow may be found again in the heat; that the figures formed in the melted wax for shocks of less intensity furnish a kind of diagram of the distribution of the heat and of the deformation in the interior of the bar, but that the calculation of the coefficient of efficiency does not yield satisfactory results in the case of moderate blows.--_Comptes Rendus_.

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TIN IN CANNED FOODS.

[Footnote: Read at an evening meeting of the Pharmaceutical Society, March 5, 1884.]

By PROFESSOR ATTFIELD, F.R.S., ETC.

From time to time, during the past twelve years, paragraphs have appeared in newspapers and other periodicals tending in effect to warn the public at least against the indiscriminate use of canned foods. And whenever there has been any foundation in fact for such cautions, it has commonly rested on the alleged presence and harmfulness of tin in the food. At the worst, the amount of tin present has been absurdly small, affording an opportunity for one literary representative of medicine to state that before a man could be seriously affected by the tin, even if it occurred in the form of a compound of the metal, he would have to consume at a meal ten pounds of the food containing the largest amount of tin ever detected.

But the greatest proportions of tin thus referred to are, according to my experiments, far beyond those ever likely to be actually present in the food itself in the form of a compound of tin; present, that is to say, on account of the action of the fluids or juices of the food on the tin of the can. Such action and such consequent solution of the tin, and consequent admixture of a possibly assimilable compound of tin with the food, in my opinion never occurs to an extent which in relation to health has any significance whatever. The occurrence of tin, not as a compound, but as the metal itself, is, if possible, still less important.

During the last fifteen years I have frequently examined canned foods, not only with respect to the food itself as food, and to the process of canning, but with regard to the relation of the food to, or the influence if any of the metal of, the can itself. So lately as within the past two or three months I have examined sixteen varieties of canned food for metals, with the following results:

Decimal parts of a grain of tin (or other foreign metal) present in Name of article a quarter of a lb. examined.

Salmon none. Lobsters none. Oysters 0.004 Sardines none. Lobster paste none. Salmon paste none. Bloater paste 0.002 Potted beef none. Potted tongue none. Potted "Strasbourg" none. Potted ham 0.002 Luncheon tongue 0.003 Apricots 0.007 Pears 0.003 Tomatoes 0.007 Peaches 0.004

These proportions of metal are, I say, undeserving of serious notice. I question whether they represent more than the amounts of tin we periodically wear off tin saucepans in preparing food--a month ago I found a trace of tin in water which had been boiled in a tin kettle--or the silver we wear off our forks and spoons. There can be little doubt that we annually pass through our systems a sensible amount of such metals, metallic compounds, and other substances that do not come under the denomination of food; but there is no evidence that they ever did or are ever likely to do harm or occasion us the slightest inconvenience. Harm is far more likely to come to us from noxious gases in the air we breathe than from foreign substances in the food we eat.

But whence come the much less minute amounts of tin--still harmless, be it remembered--which have been stated to be occasionally present in canned foods? They come from the minute particles of metal chipped off from the tin sheets in the operations of cutting, bending, or hammering the parts of the can, or possibly melted off in the operations necessary for the soldering together of the joints of the can. Some may, perhaps, be cut, off by the knife in opening a can. At all events I not unfrequently find such minute particles of metal on carefully washing the external surfaces of a mass of meat just removed from a can, or on otherwise properly treating canned food with the object of detecting such particles. The published processes for the detection of tin in canned food will not reveal more than the amounts stated in the table, or about those amounts; that is to say, a few thousandths or perhaps two or three hundredths of a grain, if this precaution be adopted. If such care be not observed, the less minute amounts may be found. I did not detect any metallic particles in the twelve samples of canned food just mentioned, but during the past few years I have occasionally found small pieces of metal, perhaps amounting in some of the cases to a few tenths of a grain per pound. Now and then small shot-like pieces of tin, or possibly solder, may be met with; but no one has ever found, to my knowledge, such a quantity of actual metallic tin, tinned iron, or solder as, from the point of view of health, can have any significance whatever.

The largest amount of tin I ever detected in actual solution in food was in some canned soup, containing a good deal of lemon juice. It amounted to only three-hundredths of a grain in a half pint of the soup as sent to table. Now, Christison says that quantities of 18 to 44 grains of the very soluble chloride of tin were required to kill dogs in from one to four days. Orfila says that several persons on one occasion dressed their dinner with chloride of tin, mistaking it for salt. One person would thus take not less than 20 to 30 grains of this soluble compound of tin. Yet only a little gastric and bowel disturbance followed, and from this all recovered in a few days. Pereira says that the dose of chloride of tin as an antispasmodic and stimulant is from 1/16 to ½ a grain repeated two or three times daily. Probably no article of canned food, not even the most acid fruit, if in a condition in which it can be eaten, has ever contained, in an ordinary table portion, as much of a soluble salt of tin as would amount to a harmless or useful medicinal dose.

Metallic particles of tin are without any effect on man. A thousand times the quantity ever found in a can of tinned food would do no harm.

Food as acid as say ordinary pickles would dissolve tin. Some manufacturers once proposed using tin stoppers to their bottles of pickles. But the tin was slowly dissolved by the acid of the vinegar. These pickles, however, had a distinctly nasty "metallic" flavor. The idea was abandoned. Probably any article of food containing enough tin to disagree with the system would be too nasty to eat. Purchasers of food may rest assured that the action taken by this firm would be that usually followed. It is not to the interest of manufacturers or other venders to offend the senses of purchasers, still less to do them actual harm, even if no higher motive comes into force.

In the early days of canning, it is just possible that the use of "spirits of salt" in soldering may have resulted in the presence of a little stannous, plumbous, or other chloride in canned food; but such a fault would soon be detected and corrected, and as a matter of fact, resin-soldering is to my knowledge more generally employed--indeed, for anything I know to the contrary, is exclusively employed--in canning food. Any resin that trained access would be perfectly harmless. It is just possible, also, that formerly the tin itself may have contained lead, but I have not found any lead in the sheet tin used for canning of late years.

In conclusion: 1. I have never been able to satisfy myself that a can of ordinary tinned food contains even a useful medicinal dose of such a true soluble _compound_ of tin as is likely to have any effect on man. 2. As for the metal itself, that is the filings or actual metallic particles or fragments, one ounce is a common dose as a vermifuge; harmless even in that quantity to man, and not always so harmful as could be desired to the parasites for whose disestablishment it is administered. One ounce might be contained in about four hundredweight of canned food. 3. If a possibly harmful quantity of a soluble compound, of tin be placed in a portion of canned food, the latter will be so nasty and so unlike any ordinary nasty flavor, so "metallic," in fact, that no sane person will eat it. 4. Respecting the globules of solder (lead and tin) that are occasionally met with in canned food, I believe most persons detect them in the mouth and remove them, as they would shots in game. But if swallowed, they do no harm. Pereira says that metallic lead is probably inert, and that nearly a quarter of a pound has been administered to a dog without any obvious effects. He goes on to say that as it becomes oxidized it occasionally acquires activity, quoting Paulini's statement that colic was produced in a patient who had swallowed a leaden bullet. To allay alarm in the minds of those who fear they might swallow pellets of solder, I may add that Pereira cites Proust for the assurance that an alloy of tin and lead is less easily oxidized than pure lead. 5. Unsoundness in meat does not appear to promote the corrosion or solution of tin. I have kept salmon in cans till it was putrid, testing it occasionally for tin. No trace of tin was detected. Nevertheless, food should not be allowed to remain for a few days, or even hours, in saucepans, metal baking pans, or opened tins or cans, otherwise it _may_ taste metallic. 6. Unsound food, canned or uncanned, may, of course, injure health, and where canned food really has done harm, the harm has in all probability been due to the food and not to the can. 7. What has been termed idiosyncrasy must also be borne in mind. I know a man to whom oatmeal is a poison. Some people cannot eat lobsters, either fresh or tinned. Serious results have followed the eating of not only oatmeal or shell fish, but salmon and mutton; _hydrate_ (misreported _nitrate_) of tin being gratuitously suggested as being contained in the salmon in one case. Possibly there were cases of idiosyncrasy in the eater, possibly the food was unsound, possibly other causes altogether led to the results, but certainly, to my mind, the tin had nothing whatever to do with the matter.

In my opinion, given after well weighing all evidence hitherto forthcoming, the public have not the faintest cause for alarm respecting the occurrence of tin, lead, or any other metal in canned foods.--_Phar. Jour, and Trans., March 8, 1884, p. 719_.

[In reference to Prof. Attfield's statement contained in the closing paragraph, we remark: It is well known that mercury is an ingredient of the solder used in some canning concerns, as it makes an easier melting and flowing solder. In THE SCIENTIFIC AMERICAN for May 27, 1876, in a report of the proceedings of the New York Academy of Science, will be seen the statement of Prof. Falke, who found metallic mercury in a can of preserved corn beef, together with a considerable quantity of albuminate of mercury.--EDS. S.A.]

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VILLA AT DORKING.

The house shown in the illustration was lately erected from the designs of Mr. Charles Bell, F.R.I.B.A. Although sufficiently commodious, the cost has been only about 1,050_l_.--_The Architect_.

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Valerianate of cerium in the vomiting of pregnancy is recommended by Dr. Blondeau in a communication to the _Societe de Therapeutique_. He gives it in doses of 10 centigrammes three times a day.--_Medical Record_.

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TECHNICAL EDUCATION IN AMERICA.

If there is one point more than another in which the exuberant youth and vitality of the American nation is visible it is in that of education, the provision for which is on a most generous scale, carried out with a determination at which the older countries of the Eastern Hemisphere have only arrived by slow degrees and painful experience. Of course the Americans, being young, and having come to the fore, so to speak, full-fledged, have been able to profit by the lessons which they have derived from their neighbors--though it is none the less to their credit that they have profited so well and so quickly. Technical and industrial education has received a more general recognition, and been developed more rapidly, than the general education of the country, partly for the reason that there is no uniform system of the latter throughout the States, but that each individual State and Territory does that which is right in its own eyes. The principal reason, however, is that to possess the knowledge, how to work is the first creed of the American, who considers that the right to obtain that knowledge is the birthright of every citizen, and especially when the manual labor has to be supplemented by a vigorous use of brains. The Americans as a rule do not like heavy or coarse manual labor, thinking it beneath them; and, indeed, when they can get Irish and Chinese to do it for them, perhaps they are not far wrong. But the idea of idleness and loafing is very far from the spirit of the country, and this is why we see the necessity for industrial education so vigorously recognized, both as a national duty, and by private individuals or communities of individuals.

From whatever source it is provided, technical education in the United States comes mainly within the scope of two classes of institutions, viz., agricultural and mechanical colleges; although the two are, as often as not, combined under one establishment, and particularly it forms the subject of a national grant. Indeed, it may be said that the scope of industrial education embraces three classes: the farmer, the mechanic, and the housekeeper; and in the far West we find that provision is made for the education of these three classes in the same schools, it being an accepted idea in the newer States that man and woman (the housekeeper) are coworkers, and are, therefore, entitled to equal and similar educational privileges. On the other hand, in the more conservative East and South, we find that the sexes are educated distinct from each other. In the East, there is generally, also, a separation of subjects. In Massachusetts, for instance, the colleges of agriculture and mechanics are separate affairs, the students being taught in different institutions, viz., the agricultural college and the institute of technology. In Missouri the separation is less defined, the School of Mines and Metallurgy being the, only part that is distinct from the other departments of the University.

One of the chief reasons for the necessity for hastening the extension of technical education in America was the almost entire disappearance of the apprenticeship system, which, in itself, is mainly due to the subdivision of labor so prevalent in the manufacture of everything, from pins to locomotives. The increased use of machinery, the character of which is such as often to put an end to small enterprises, has promoted this subdivision by accumulating workmen in large groups. The beginner, confining himself to one department, is soon able to earn wages, and so he usually continues as he begins. Mr. C.B. Stetson has written on this subject with great force and earnestness, and it will not be amiss to quote a sentence as to the advantages enjoyed by the technically workman. He says that "it is the rude or dexterous workman, rather than the really skilled one, who is supplanted by machinery. Skilled labor requires thinking; but a machine never thinks, never judges, never discriminates. Though its employment does, indeed, enable rude laborers to do many things now which formerly could only be done by dexterous workmen, it is clear that its use has decidedly increased the relative demand for skilled labor as compared with unskilled, and there is abundant room for an additional increase, if it is true, as declared by the most eminent authority, that the power now expended can be readily made to yield three or four times its present results, and ultimately ten or twenty times, when masters and workmen can be had with sufficient intelligence and skill for the direction and manipulation of the tools and machinery that would be invented."

The establishment of colleges and universities by the aid of national grants has depended very much for their character upon the industrial tendencies of the respective States, it being understood that the land grants have principally been given to those of the newer States and Territories which required development, although some of the institutions of the older States on the Atlantic seaboard have also been recipients of the same fund, which in itself only dates from an act of Congress in 1862. In California and Missouri, both States abounding in mineral resources, there are courses in mining and metallurgy provided in the institutions receiving national aid. In the great grain-producing sections of the Mississippi Valley the colleges are principally devoted to agriculture, whereas the characteristic feature of the Iowa and Kansas schools is the prominence given to industries.