tained and allowance made for it, so that accurate measurements can always be made with it when it is worn.

In the micrometer gauge the wearing surfaces are so arranged that they can be adjusted with ease in a few moments. The wear between the male and female parts of the micrometer can be adjusted by a binding-screw. This adjustment can be repeated as often as required, so that the instrument will read with great accuracy until it is worn out.

Your committee assured themselves, by actual trial, that with such a gauge boys can very easily be taught to read the thousandth of an inch or the fortieth of a millimeter, and that it is practicable to read even the eightieth of a millimeter.

The micrometer gauge is of these last two gauges the simplest. It consists of a micrometer screw, C, with a vernier attachment on D, is susceptible of easy adjustment, is not likely to wear, is not complicated, is less likely to get out of order than the other gauges, is more easily read, and requires less skill to read it than the sliding gauge with a vernier. Your committee are, therefore, of the opinion that this gauge, which is shown in the annexed cut, is the gauge which should be adopted as the standard gauge.

They are of the opinion that all gauges should be graduated so as to read fractions of an inch or of a millimeter, and that the sizes should be directly expressed as the only means of insuring correct measurements, and not by numbers, which constantly lead to error. That this, while it insures great accuracy, presents no difficulty in practice, is shown by a number of experiments made during a period of several months, to ascertain the practical difficulty in the way of the adoption of this method by a member of your committee. The sizes of some of the steel bars, the orders for which were expressed in thousandths of an inch, are given below.

Sizes expressed in Decimals of an Inch, taken at random from the Order-book

The trial of this system by some of the manufacturers has resulted in banishing all the old forms of gauge from their workshops.

The conclusions which have been arrived at, for the most part independently, by the different members of your committee, and in which they unanimously agree, are:

1. The abandonment of the system of fixed gauges for commercial use.

2. The abandonment of the system of representing the diameters and sizes by numbers.

3. The adoption of the system of expressing sizes in thousandths of an inch or fractions of a millimeter.

4. The adoption of the micrometer gauge as the method of measuring sizes.

Your committee beg to acknowledge their indebtedness to J. B. Knight, Secretary of the Franklin Institute in Philadelphia, for the reports of various committees on gauges to the Franklin Institute; to C. Hewitt, Esq., President of the Trenton Iron Company, for a large number of measurements of wire made with different gauges; to P. Ritter Von Tunner, of Austria, for the description of the kind of gauges used in Austria; to the German Consul, for his interest in procuring from Germany a report of their gauge system; to the French Consul, for his interest in the work of the committee; and to the Minister of Agriculture, Commerce, and Public Works, for a complete description of the gauge system as used in France.

Your committee is, however, particularly indebted to Darling, Brown & Sharp, of Providence, who have loaned to them without charge all the gauges which they manufacture, for comparison, and have contributed besides a very large amount of information on various matters connected with this subject. All of which is respectfully submitted. T. EGLESTON, Chairman. WM. METCALF,

Jos. D. WEEKS.

ANALYSES OF SOME TELLURIUM MINERALS.

BY E. P. JENNINGS, CORNELL UNIVERSITY, ITHACA, N. y.

(Read at the Amenia Meeting, October, 1877.)

THE abundance and value of the tellurium minerals of Colorado is well known, but, as yet, few analyses have been made of them, and I offer these as a small contribution to the chemistry of these valuable ores.

1. Native Tellurium.-The specimens from which the analyses of this mineral were made are from the "John Jay" Mine, Boulder County, Colorado, where it occurs in quite large masses, though mixed with more or less silica and iron pyrites. It is usually a finegrained, tin-white mineral, but sometimes occurs in distorted, hexagonal prisms in cavities in the quartz. Before the blowpipe it gives the reactions for tellurium, sulphur and iron; by cupellation, it yields a small amount of gold. An analysis of a coarsely crystallized specimen gave the following results:

Deducting the pyrites, iron oxide and silica, we have for the composition of the mineral:

Tellurium,.

Gold,

97.73

2.27

100.00

Or, considering the gold to be in combination with tellurium to

form sylvanite, we have:

Native tellurium,

Sylvanite (Au, Tez), ⋅

95.50

4.50

100.00

An analysis of another specimen from the same mine, and of but slightly different appearance, gave the following results :

Deducting the silica, pyrites and oxide of iron, we have for the composition of the mineral:

Assuming the mineral to be a mixture of native tellurium, sylvanite and altaite, we will have:

Native tellurium,
Sylvanite (Au, Teg),
Altaite (Pb Te),

73.21

17.46

9 33 100.00

2. Sylvanite.—I have analyzed only a single specimen of this mineral, obtained from the Smuggler Mine, Boulder County, Colorado. In appearance it resembles somewhat the native tellurium from the John Jay Mine, but is more of a lead-gray color, and is not so finegrained. Before the blowpipe it gives the reactions for tellurium and gold, the gold being light-colored from the large amount of silver it contains.

Deducting the silica, oxide of iron and alumina, and assuming the small amount of zinc to be combined with tellurium, we have:

which agrees closely with the formula of sylvanite (Au,Ag),Te̱.

ON PULVERIZED ZINC AND ITS USES IN ANALYTICAL CHEMISTRY.

BY DR. T. M. DROWN, LAFAYETTE COLLEGE, EASTON, PA.

(Read at the Philadelphia Meeting, February, 1878.)

ZINC is, as is well known, very brittle at a temperature of about 210° C. (410° F.), and may then be readily pulverized in a mortar. By sifting it may be obtained of uniform grain. I have been accustomed to prepare products passing through 40, 60, and 80-mesh sieves, and also by bolting through a fine handkerchief.

The principal analytical uses to which I have hitherto applied this material are to the reduction of iron directly from the ore by heating it with the pulverized zinc, and the reduction of ferric to ferrous compounds in solution.

In the first case the pulverized ore, 0.5-gram or less, is intimately mixed with about ten times its weight of the pulverized zinc (the finer the zinc the better), in a porcelain crucible, and this mixture is covered with about the same amount of zinc. The crucible is then heated at the top of the flame of a Bunsen burner, at a dull red heat, for about ten minutes. The crucible should not be covered. When cool, the crucible, with its contents, is placed in a flask treated with hot dilute sulphuric acid, and brought quickly to a boil. The zinc and reduced iron are dissolved in a few minutes and the flask is then tightly corked and allowed to cool. When cool, the iron is directly titrated by potassium permanganate.