-saponin or an allied vegetable alkali. These plants also furnish many useful medicines, and not unfrequently highly nutritious food. The poisonous principle is readily expelled by heat, as in the manihot or jatropha, whence the cassova and tapioca are derived.

Dr. Stevens. This is the bread fruit of Brazil, and I have seen the natives preparing it for use. The plant resembles very closely our sassafras; it has the same rough bark and the same palmate leaf. The food is derived from the root, and it probably produces a larger amount of food from a given area of ground than any other plant. A yield of 3,000, 4,000, and 5,000 bushels to the acre is not uncommon, and the cultivation is of the roughest kind. In fact, it has no cultivation except planting. The universal South American knife, the machete, is used to cut a hole in the sod, the plant is inserted, and left to take its chance. It is sure to take its chance, however. It will root out all other plants, and it cannot itself be destroyed. The root is grated in mills, the milk flows away, and the pulp is dried for food. The milk is wasted by the hogshead; I have seen a river white with it for a long distance below the grating mill. This milk is poisonous, and it contains the saponaceous principle. The women use it freely for washing their persons, and I am bound to say, that during the bread fruit harvest is the only time of year that they are clean. Prof. Seely. I will say a word in regard to soft soap. Genuine soft soap, such as I knew in my boyhood, is not now to be found. This was made by the farmers from the ashes of their wood fires. The ashes were placed in a barrel, and leached by pouring water upon them from time to time, and then the lye was boiled with grease to make soft soap. Now farmers come into the city and buy something under the name of soft soap; but it is nothing but a little hard soap with a great deal of water and a little salsoda. It would be much more economical to buy the hard soap without the water.

On motion of Mr. Fisher, the subject of "Printing in Colors" was adopted for the meeting two weeks hence. Adjourned.

THOMAS D. STETSON, Secretary.

AMERICAN INSTITUTE POLYTECHNIC ASSOCIATION,
22, 1862.

The Chairman, Prof. CHAS. A. Joy, presiding.

The only miscellaneous business introduced was the presentation to the society of J. W. Nystrom's book containing an exposition of his

NEW SYSTEM OF ARITHMETIC,

with sixteen for the base in place of ten in the present decimal system. The work was referred to a committee, consisting of Mr. Stetson, Prof. Seely and Mr. Dibben, and the society proceeded to the discussion of the regular subject of the evening:

PRINTING IN COLORS.

Mr. Fisher.—It is well known that the success in printing in colors has been very imperfect, and I suppose that this is owing to the want of artistic knowledge and taste on the part of the operators. Brewster ascertained that all colors are formed by the combination of three: red, yellow and blue, which he called the primary colors. Now, I suppose that if these three were properly blended, all colors and all shades of color might be produced. Perhaps black might also be employed with advantage. I suppose that nine-tenths of the colors and shades employed in portrait painting might be produced from red, blue and black.

Dr. Stevens.-Probably the man who first printed in colors was Faust. Before the art of printing with movable types was invented it was customary to ornament the manuscript books with illuminated letters of various colors, and in order to make the printed books as nearly like those in use as possible, the printers undertook to print their initial letters in colors, and they produced some very fine results. But the practice after a while fell into disuse. At the present time, printing in colors is carried on in this country with very satisfactory results, though not so well as in England and Germany. Maps especially are printed in this way, so as to rival those colored by hand. Prof. Rogers, formerly of this country, but at present of Edinburgh, had a geological map printed in this way, which is nearly, if not quite, equal to any colored by hand. Each color is put on by a separate stone; though after all of the sheets are printed in one color from a stone, the color may be wiped off, and the same stone may then be prepared for another color, with which all of the sheets may be printed.

Mr. Gavitt.—Mr. President: I received your invitation so short a time before the meeting that I have made no preparation, and my remarks must be very desultory. The American Bank Note company print their bills in colors as a guard against counterfeiting by the photographic process. If a bill is printed partly in red, the counterfeiting photographer must remove the red before he photographs the rest of the bill, and the red must then bo printed in. The colors formerly used could all be readily removed, but it was suggested by one of the most eminent chemists in the world, Mr. Sterry Hunt, that the sesquioxyd of chromium would be found as permanent as the black carbon ink. We have accordingly adopted this pigment, and hence the great quantity of green you see in modern bank notes, especially in the United States treasury notes. The sesquioxyd of chromium resists the action of all acids except boiling nitric acid, and that destroys the texture of the bill. The only way in which it can be removed is by saponifying the oil which is employed as a medium to attach it to the paper, and as the same medium is used for the carbon ink, if one is removed they both go together. We print the green over the black, and this we consider a perfect safeguard against counterfeiting by photography.

Prof. Seely. I think, Mr. Chairman, that this apprehension of counterfeiting by photography is a bugbear. I have frequently heard of bank notes that were counterfeited by photography, and I have been told that if I would go to this place or that place, I should see one so perfect that it could not be distinguished from the genuine note. The narrators seem not

to have considered that this fact would destroy the evidence of its being a counterfeit. If it could not be distinguished from the genuine bill, how can it be known that it is not genuine? And I presume that in most of the cases in which it was supposed that bills had been counterfeited by photography, genuine bills were mistaken for counterfeits. I have seen photographs of bank notes; I have made some myself, but I never saw one that could not be readily detected, or that had been in circulation. Here is a bill printed wholly in black, and there are a great many such in circulation. If it is so easy to photograph black notes, why are not these counterfeited? It must be either because photographers are not able to do it, or because they are all too honest.

Mr. Gavitt.—Mr. Chairman, I will ask Prof. Seely one question. Here is a bank note with the letters, ONE, in red; now, is it more difficult to photograph that note than it would be if those letters were printed in black?

Prof. Seely. It is more difficult, certainly.

Mr. Gavitt. Very well, Mr. Chairman, that is sufficient. I hold that it is the duty of bank officers to furnish the community with every possible safeguard against the danger of being swindled by false notes, and if it is in any degree more difficult to counterfeit a note printed in colors, then all notes should be printed in colors, without any regard to the expense. I agree with Prof. Seely that the danger of circulating photographs of bank notes is a bugbear, but photography may be employed to produce lithographs of bank notes, which are the most dangerous counterfeits. There was a publication of a bank note detector started a few years ago on a new plan. It was to have fac-similes on a small scale of all the genuine bank notes in the country. You probably remember the work. Photographs were taken of just one-sixth the size of the bills, and then these were transferred to stone by the photo-lithographic process, and the bills were then printed from the stone. The photographs were made by Mr. Rehn, one of the most skillful photographers in the world, and the prints were perfect copies of the bills. It was only necessary to take a glass that would magnify just six times, and you had the exact thing. The most delicate lines were all reproduced with wonderful accuracy. Some of these lines, being so much reduced in size, were absolutely finer than the fiber of the paper, and we were obliged to have a cardboard surface in order to print them. But, of course, if not reduced, they might be printed on bank note paper. Counterfeiting by photography is a bugbear, but not by photo-lithography. Mr. Rowell. Have any of the United States treasury notes been counterfeited?

Mr. Gavitt. They have not.

The Chairman.-How much of the sesquioxyd of chromium is used for bank note printing?

Mr. Gavitt.-Nearly all that is used is used by the American Bank Note company. We have consumed about 10,000 pounds within the last three years. It costs about a dollar a pound in large quantities.

The Chairman.-There is a process of printing in colors practiced in Germany, called nature printing. A natural object-a leaf, for instanceis placed under a thin sheet of pure lead, and passed between rollers. The

leaf is pressed into the lead, forming a mold for an electrotype plate, which is employed for printing. Inks of the proper color are used in the printing, and where several colors are required they are worked on the same plate, so as to print the whole at one impression. The Consul-General of Austria, Charles F. Loosey, presented several magnificent volumes of these prints to the American Institute a few years ago. It was a most valuable and acceptable donation, and I trust was properly recognized and appreciated. A volume of the prints was brought from the library, and greatly admired by those present.

The subject of "Illuminating Materials" was selected for the next meeting, and the society adjourned.

THOMAS D. STETSON, Secretary.

AMERICAN INSTITUTE POLYTECHNIC ASSOCIATION,
May 29, 1862,

The Chairman, Prof. CHAS. A. Joy, presiding.
The Chairman announced the regular subject of the evening to be

ILLUMINATING MATERIALS,

and, as he proposed the subject, he proceeded to open the discussion.

}

Illuminating materials are found in all three forms of matter; solid, liquid and gaseous. They generally contain hydrogen and carbon, and the light is emitted by the carbon while it is in an incandescent state, after it is heated by the burning of the hydrogen, and before it is itself consumed. I have in my hand a list of some 16 or 18 materials which have been used for producing light.

This has been used from time immemorial.

One of these is tallow. Some of the vegetable oils have also been used from the most ancient times of which we have any knowledge; among these are palm oil and olive oil, In Greece, 2,000 years ago, they used lamps essentially the same as those which are used in some countries at the present day. I hold in my hand an earthen lamp that was dug from the ruins of Athens. It has a handle upon this side and this is the place for the wick. The material burned in it was probably olive oil. It differs, you see, but very little from the lamps which. we use, and all over Germany the workmen use lamps precisely like this, only their lamps are made of tin.

Dr. Stevens.-Earthen lamps are used extensively in the western part of this country.

The Chairman.-The kind of fat, either animal or vegetable, used for illuminating in any country, is determined by the supply; it is a mere question of economy.

Besides the hydrocarbon compounds, there is a class of substances of a different character employed for the production of light. Among these are lime in oxyhydrogen light; the carbon points for the electric light; magnesium and quicksilver.

Magnesium produces one of the most intense lights that we have. It is only necessary to light the end of a very small wire of pure metallic magnesium in an alcohol flame, when the wire is consumed, giving out a very brilliant light. I have tried the experiment, but it is a disagreeable one to perform, on account of the effect of the light upon the eyes. It is some

time after looking at the magnesium flame before the eye is able to see ordinary objects in a room. The experiment should not be tried without providing protection for the eyes. The light in this case comes from the oxyd of magnesium. The metal combines rapidly with oxygen, generating a heat which makes the oxyd formed, the magnesia, incandescent, and it is this white hot magnesia that emits the light. The magnesium light might be utilized by winding a long wire of the metal upon a reel or bobbin, and unrolling the bobbin to feed forward the wire as it is consumed, were it not for the high cost of the metal. It exists in large quantities, especially in this country. At Hoboken there are deposits of porphyry which contain magnesia, and in Westchester county are beds of dolamite, composed to a large extent of magnesia. Magnesium is abundant; the difficulty is to separate it from the oxygen and other substances with which it is combined.

Quicksilver is used to conduct a stream of electricity.

Mr. Babcock.-I should like to hear the chairman's account of the Drummond light.

The Chairman. I spoke of that in passing. It is very improperly called the calcium light-there is no calcium in it except as lime, the oxyd of calcium. The oxyhydrogen light is formed, as you are probably all aware, by heating a bit of lime in the flame of the oxyhydrogen jet. The lime must be chemically pure, and it is consequently necessary to prepare it for the purpose. It is precipitated from a solution, and thus obtained free from silica or any other substance. It is then pressed in a powerful hydraulic press, in order to make it hard enough to be sawed into pieces of suitable size. Lime is used because it cannot be fused, and under the intense heat of the oxyhydrogen jet, it gives out the brilliant light with which you are familiar. The oxyhydrogen flame is formed by burning pure hydrogen gas in pure oxygen. The gases are retained in separate vessels, and are mixed just as they issue from the pipes. The hydrogen pipe surrounds that which conducts the oxygen, and the oxygen pipe is now made to protrude a very little beyond the end of the hydrogen pipe. This is the latest improvement in the oxyhydrogen light.

Dr. Stevens.-The chairman forgot to mention one substance in his list of illuminating materials-bayberry tallow This is used to a considerable extent. It is a vegetable tallow, produced by the bayberry bush.

Mr. Stevens.-The Balm of Gilead tree produces a tallow which has been collected and made into candles. Each bud has a small quantity of tallow, and if the buds are placed in hot water, the tallow is melted, and may be skimmed from the surface. I have collected a very little of this myself, and I have heard my mother say that she and her mother collected one year enough to serve for light for several months.

The Chairman.-Will Prof. Seely give us the chemistry of illuminating materials?