of the car completely from the outside air has been generally abandoned. The ice-cooled cars now in use are usually provided with an arrangement which draws in air from the outside and sends it, after cooling it by contact with the ice, to renew the air in the car. The free space remaining for the disposition of the merchandise is about 30 to 40 cubic feet, allowing the introduction of a load of from 6 to 10 tons, according to the nature of the products. By an ice consumption of an average of 400 kilograms per day a temperature varying between 8° and 4° C. is obtained. The degree of humidity is high, however.

The cars cooled by evaporation of a liquid gas (in this case aminonia) carry on the outside two cylindrical tanks of liquid ammonia. This fluid is sent by regulating cocks into coils placed at the two ends of the car on the inside. The ammonia evaporates and absorbs heat, the ammonia gas produced dissolving in water in a tank placed under the car. One car of this variety was experimented with in 1905 in the transportation of butter from Siberia. The cost of refrigeration for butter maintained at a temperature of from 4° to 5° C. was as high as 0.068 franc per kilogram of butter per day.

In the ice-cooled cars of various types experimented with by the same Russian commission the total cost of refrigeration, including all expenses (ice consumption and charging, installation of ice houses, and operation of cars), amounted to 0.009 francs per kilogram of butter.

As the short summary I have just made shows, the First International Congress of Refrigeration has examined with care most of the scientific and technical problems which exist in the refrigerating industry. If it has solved any of these problems it has indicated in the form of resolutions a very great number of others which up to the present have been only incompletely worked out. The next international congress, which will be held in Vienna in 1910, will not be inferior to that at Paris, and will bring us, let it be hoped, in the scientific phase, to some accurate knowledge of the properties of bodies at low temperatures, and in the industrial phase to a uniformity of units of measure and methods of testing machines and insulating material.

THE NITROGEN QUESTION FROM THE MILITARY

STANDPOINT."

By CHARLES E. MUNROE,

Professor of Chemistry, The George Washington University.

.

The invention of gunpowder afforded man a means of utilizing the energy of chemical separation in effecting propulsion and of more efficiently applying this form of energy in mining and quarrying. Through the discovery or invention of mercuric fulminate, the cellulose nitrates, the glyceryl nitrates, the nitro-substitution compounds, and the various explosive compositions made from these nitrates and nitro-compounds, man was enabled also to utilize the energy stored up in unstable molecules. History indicates that the invention of gunpowder was made where saltpeter, which is its chief ingredient, was naturally most abundant and most easily obtained, but that, owing to the great value of gunpowder to man, its use and manufacture spread to the cooler and more humid countries, and it is in these countries that it and the other explosives enumerated have come to be most extensively used. Statistics are not at hand by which to show the increase in the use of powder throughout the world, but some relative idea of this growth in recent years may be gained from Table 1, which sets forth the quantity, or value, or both, of the gunpowder, including, since 1860, blasting powder also, produced in the United States in each census year beginning with 1840.

The statistics for the world's production of the modern explosives are also not accessible, but an item contributing toward the assembling of this valuable information regarding the world's progress was given for dynamite as sold from the several factories with which Alfred Nobel, the inventor of dynamite, was associated, though as there were, during the period covered, independent factories in Germany, in America, and probably in other countries, these figures, as set forth in Table 2, give only a relative idea of the growth of this industry.

a Reprinted by permission from United States Naval Institute Proceedings, vol. 35, No. 3. Copyright, 1909, by Philip R. Alger, secretary and treasurer, United States Naval Institute.

a Chemicals and Allied Products, Bulletin 92, Census of Manufactures for 1905, by Charles E. Munroe, p. 82.

Not reported.

TABLE 2.-Annual sales of dynamite from Nobel factories.a

a Notes on Nitroglycerin, Dynamite, and Blasting Gelatine, by George McRoberts, Phil. Soc. Glasgow April 25, 1883.

TABLE 3.—Quantities and values of explosives produced in the United States in the census years 1900 and 1905.a

a Chemicals and Allied Products, Bulletin 92, Census of Manufactures for 1905, by Charles E. Munroe,

p. 80.

A keg contains 25 pounds of blasting powder.

e Including 31,661,806 pounds, produced and consumed, valued at $4,749,271.

d Including 43,643,270 pounds, produced and consumed, valued at $6,110,058.

• Including 2,139,834 pounds, produced and consumed, valued at $1,069,917. 1 Including 5,522,796 pounds, produced and consumed, valued at $2,209,118.

The most complete and detailed figures relative to the production of explosives to be found anywhere are those presented in the reports on the census of manufactures of the United States for 1900 and 1905, which are as follows, the gunpowder and blasting powder, which were combined in Table 1, being presented separately in Table 3.

It is an interesting and important fact that, as with gunpowder so with all of the other explosives enumerated, a nitrogen-containing compound is employed in the manufacture of each and nitrogen remains as a component or constituent of each product. The quantity of nitrogen in one hundred parts of these explosives, together with its equivalent in real nitric acid and in sodium nitrate, is shown, together with other data relative to these explosives, in the following table:

TABLE 4.-Per cent of nitrogen in certain of the more important explosives.

In calculating the data for Table 4 the gunpowder is assumed to be composed of KNO,, 75 per cent; C, 15 per cent; S, 10 per cent; and the blasting powder of NaNO3, 74 per cent; C, 16 per cent; S, 10 per cent; but variations from these compositions will be found in practice. However, it is believed that they represent very closely the averages of all commercial compositions so styled. Although a most important explosive, dynamite is omitted from the table because the wide variations in the character and quantities of the components of this mixture as it occurs in commerce render it impossible to properly represent it by an average formula, though it is usually admitted that on the average dynamite contains 40 per cent of nitroglycerol. The wide variation in nitrogen contents occurs in the dope or absorbent, which may contain from no nitrogen-containing com

ponent whatever, as in the kieselguhr dynamites, to 60 per cent of sodium nitrate in straight wood-pulp dynamites; and this last material may be partly or wholly replaced by ammonium or potassium or cellulose nitrates in other dopes and compositions. Because of a similar wide variation in their components the compositions made from picric acid, its salts, and other nitro-substitution compounds are also omitted. Notwithstanding these omissions, it is believed that the data set forth in the table may prove useful in the development and checking of the statistics of manufacture. But, unfortunately, owing to the different manners in which the nitrogen atoms are grouped, as regards the other atoms, in the molecules of the different kinds of explosives, no direct relation is to be observed between the properties and behavior of these different bodies and the percentages of nitrogen they contain, and this want of relation becomes the more marked the larger the number of different nitrogencontaining substances that we consider. What, however, is emphasized by this presentation of data, is that the element nitrogen is a characteristic and important component of all explosives that have been accepted and used for military purposes.

From the time of the invention of gunpowder until the middle of the last century the only recognized available source of this nitrogen was India saltpeter, which is the potassium nitrate, and which was obtained from the niter found or formed in soil or rocks. The production of nitrates in the soil or rocks is brought about usually through the agency of nitrifying bacteria. In order that the process of nitrification may go on there is required a supply of nitrogenous organic matter, a slightly alkaline medium, a temperature range between definite limits, a limited amount of moisture, a supply of oxygen or air, complete or semi darkness, and the presence of the nitrifying organisms. The nitrification proceeds most rapidly at 100° F. and within a few inches of the surface of soil or rock which is well aerated and moderately moist. When potash salts are present in sufficient quantity the potassium nitrate is produced, but the native niter usually consists largely of calcium nitrate with some magnesium nitrate and other salts. All of these nitrates are readily soluble in water and may therefore, after formation, be to a great extent washed away by frequent rainfalls, but where there is only a moderate amount of water present the solution may be brought to the surface by capillarity, and as the water evaporates the nitrates will be left as an efflorescence on the surface of the soil or rock. It is evident, therefore, that accumulations of niter will be largest in those localities where not only the best conditions for its production obtain, but where also it is least likely to be washed away after being formed. The native sources of supply are therefore found as efflorescences on the soil in semiarid countries, in limestone caverns, where the remains