of the pen. A glass tube drawn out to a fine point, well rounded in a gas flame, also acts as an efficient pen. The principal precaution necessary is to take care that the pen does not disturb the surface of the paper.

Evidence of the strength of sizing is obtained by watching the spread of the ink. With a badly sized sheet the ink tends to spread. Then the disappearance of the little ridge of ink produced by the pen, as the ink penetrates the paper, is a useful indication. With a badly sized sheet, the ridge quickly disappears. The following test can be used:

Allow one drop of ink to fall upon each of the sheets of paper to be compared; at first the drop is spherical, but after a while it becomes slightly flattened and covers a larger area. With well-sized papers the drop will retain its spherical form for a considerable period.

In the ordinary application of the test with these inks, it is usual to draw a cross, consisting of four strokes, two parallel with one another in the horizontal direction, and two parallel with one another in the vertical direction across the former.

a

b

Fig. 103. Leonhardi's Test for Sizing Qualities of Paper, with Paper shown in Position.

(a) Pipette containing chloride of iron solution.

(b) Stock of chloride of iron reagent.

(2) Leonhardi's process for estimating the sizing quality of paper is an advance upon the ink method.

A chloride of iron solution of definite strength containing 1.53 per cent. of iron, and a 1 per cent. solution of freshly prepared tannic acid, are required. (Fig. 103.)

Fit up a burette or pipette in a suitable stand, so that the lower end is about four inches from the table. Place the paper to be tested under the burette, and allow one drop of the chloride of iron solution to fall on the surface of the paper. Keep the drop on the paper for as many seconds as may be equal to the weight of the paper in grammes per square metre. Then remove any excess of solution quickly with blotting paper. Reverse the paper, and moisten with the 1 per cent. tannic acid by means of a pad of cotton wool, taking up any excess with blotting paper.

The extent of the coloration is a measure of the strength of the sizing.

Even this test is merely an empirical one, and the results obtained are of a somewhat negative character. That is to say, one can readily sort up a number of papers into two or three classes, but in the case of samples which may all happen to be well sized no effects will be produced, and in this way the test is of no service in discriminating between well-sized papers. For many purposes such a degree of refinement may be unnecessary, but it is obvious that, under special circumstances, a delicate "surface" test would be useful.

(3) Schluttig and Neumann's method for the determination of the strength of sizing in papers is an ingenious attempt to record this somewhat uncertain property by a numerical expression.

The paper is arranged upon a sloping stand, the sides of which are placed at an angle of sixty degrees. The chloride of iron is not brought upon the paper by means of a drawing-pen, but is allowed to flow from a measuring tube down a grooved plate which is placed above the paper. The solution contains 100 parts by weight of chloride of iron, one part of gum arabic and two parts of phenol. A definite quantity of the solution is employed and three lines are thus produced on

the paper, parallel with one another. The paper is left for fifteen minutes and then reversed, in such a manner that the iron chloride strokes are horizontal. On the reverse side of the paper a solution of tannic acid containing 0.2 per cent. phenol is allowed to flow in precisely the same way. (Fig. 104.)

By this means three horizontal lines of iron chloride solution on one side of the paper are crossed by three

vertical lines of tannic acid on the other, forming nine points of intersection. With papers lightly sized, the nine points of intersection appear very black, owing to the contact of the tannic acid with chloride of iron. An intense black colour appears in the paper. With better-sized papers the coloration is less marked, the chemical action taking place inside the sheet below the surface.

The cross points do not colour up equally, and the gradual development of the black colour can easily be watched. With very heavily sized papers no effect is produced at all.

#

Fig. 105.-Sizing Tests.

The authors of the process claim that they are able to detect small differences in sizing quality, and that the results of their method are in strict accordance with the effects produced by writing inks. They also claim that the penetration effect of a drop of chloride of iron allowed to fall upon the surface of the paper, as in the

method of Leonhardi, is not the same as that produced by allowing the solution to flow on at an angle of sixty degrees, as in their process. In the case of highly glazed papers penetration of the ink takes place more readily with the vertical fall of a drop of solution than with the oblique direction.

A modification of Schluttig's method can be tried by drawing three lines of different widths on one side of the paper by means of an ivory-pointed drawing-pen, using the chloride of iron solution, allowing the solution to remain on the paper a given time. The excess of solution is then removed by blotting paper which should not be pressed down, but merely brought into contact with the liquid. The paper is reversed and similar lines drawn at right angles, using tannic acid solution. This is also allowed to remain for a definite period,

Fig. 106. Sizing Test.

excess removed as before, and the development of black marks at the points of intersection watched for.

The method is represented by the conventional diagrams shown in Figs. 105, 106.

Winkler has constructed the following table (XVII.), comparing the various methods, giving a scale of degrees for the "strength of sizing.”

TABLE XVII., showing Classification of Paper for "Strength of Sizing."

Absorptive Capacity.-The capacity of a paper for absorbing moisture may be determined by one or two methods. This quality is of the greatest importance in blotting papers, filter papers and copying-papers.

A rough comparison of blotting papers is generally made by observing the effect of applying the various papers to characters written on a sheet of highly glazed paper. The general behaviour of the blotting paper when some ink is thrown upon it from a pen is also observed.

Strip tests with water. The capacity for absorption is expressed in numerical values by means of a simple appliance. Strips of blotting paper about half an inch wide and six inches long are suspended in any convenient manner.

These strips are then suspended with the lower end dipping into water, to the depth of about a quarter of an inch. The water rises rapidly at first, and then more slowly as the paper becomes saturated. The height to which the water rises in ten minutes is then noted.

In making this test it is advisable to note the time taken for every half-inch from the surface of the water. Some papers will give a rapid absorption for the first five minutes and then show a great falling off in the rate. Other papers will absorb more evenly all the time. These points should be carefully noted because they afford additional evidence as to the value of the paper.

'Strip" Method.

Dr. Klemm has constructed a scale of degrees for use in his laboratory, as shown in Table XVIII.

Strip tests with ink.-A similar test for absorbency, using Stephen's blue-black ink in place of water, affords valuable information.

This test can be still further extended by allowing the strips of blotting paper to become perfectly dry and then submitting the same strips to the ink test a second time. Poor blotting papers will show a marked reduction in the absorbency when put to this severe test.

Blot tests with ink.-Another test much used by stationers and users of blotting papers is to make a large blot on the paper and allow the blot to dry. If the paper is a good one the blot will appear even and uniform, but if te paper is defective the blot is surrounded by an outer ring of different appearance to the inner zone.

If this test is made under strictly comparative conditions some useful indications of quality can be obtained.

The test may be applied as follows:

The paper in the form of a sheet four inches square is placed under the end of a small burette containing Stephen's blue-black writing ink. The paper is so arranged on a tumbler that the blot will form freely without

Fig. 108a.-Blot of Ink produced on Paper of Good Quality.
Outer zone small.

touching the edges of the tumbler, with its surface about half an inch below the burette. A definite quantity of ink, half a cubic centimetre, is dropped on to

the paper, drop by drop, each drop being absorbed before the next is allowed to fall. The time occupied in absorbing this quantity is also noted. When the blot dries out the diameter of the rings is calculated.