Since it was discovered that the lead and manganese compounds of rosin acids had a better and more rapid action on linseed oil than the older form of driers, such as red lead, litharge, manganese dioxide, etc., the number of preparations of the former class has increased enormously. Manufacturers are continually at work endeavoring to improve the quality of these compounds, and to obtain a preparation which will be peculiarly their own. Consequently, with such a large variety of substances to deal with, it becomes a matter of some difficult}' to distinguish the good from the bad. In addition to the general appearance, color, hardness, and a few other such physical properties, there is no means of ascertaining the quality of these substances except practical testing of their drying properties, that is, one must mix the driers with oil and prove their value for oneself. Even the discovery of an apparently satisfactory variety does not end the matter, for experience has shown that such preparations, even when they appear the same, do not give similar results. A great deal depends upon their preparation; for example, manganese resinate obtained from successive consignments, and containing the same percentage of manganese, does not always give identical results with oil. In fact, variation is the greatest drawback to these compounds. With one preparation the oil darkens, with another it remains pale, or sometimes decomposition of the oil takes place in part. The addition of a small proportion of drier has been known to cause the separation of 50 per cent of the oil as a dark viscous mass. One drier will act well, and the oil will remain thin, while with another, the same oil will in the course of a few months thicken to the consistency of stand oil. These various actions may all be obtained from the same compound of rosin with a metal, the source only of the drier varying.

The liquid siccatives derived from these compounds by solution in turpentine or benzine also give widely divergent results. Sometimes a slight foot will separate, or as much as 50 per cent may go to the bottom of the pan, and at times the whole contents of the pan will settle to a thick, jelly-like mass. By increasing the temperature, this mass will become thin and clear once more, and distillation will drive over pure unaltered turpentine or benzine, leaving behind the metallic compound of rosin in its original state.

The compounds of metals with fatty acids which, in solution in turpentine, have been used for many years by var-rush-makers, show even greater variation. At the same time, a greater drying power is obtained from them than from rosin acids, quantities being equal. As these compounds leave the factory, they are often in solution in linseed oil or turpentine, and undoubtedly many of the products of this nature on the market are of very inferior quality.

The examination of these bodies may be set about in two ways:

A

By dissolving in linseed oil with or without heat.

B

By first dissolving the drier in turpentine and mixing the cooled solution (liquid siccatives) with linseed oil.

Before proceeding to describe the method of carrying out the foregoing tests, it is necessary to emphasize the important part which the linseed oil plays in the examination of the driers. As part of the information to be gained by these tests depends upon the amount of solid matter which separates out, it is essential that the linseed oil should be uniform. To attain this end, the oil used must always be freed from mucilage before being used for the test. If this cannot readily be obtained, ordinary linseed oil should be heated to a temperature of from 518° to 572° F., so that it breaks, and should then be cooled and filtered. With the ordinary market linseed oil, the amount of solid matter which separates varies within wide limits, so that if this were not removed, no idea of the separation of foot caused by the driers would be obtained. It is not to be understood from this that unbroken linseed oil is never to be used for ordinary paint or varnish, the warning being only given for the sake of arriving at reliable values for the quality of the driers to be tested.

A

Solution of Drier in Linseed Oil. —The precipitated metallic compounds of rosin (lead resinate, manganese resinate and lead manganese resinate) dissolve readily in linseed oil of ordinary temperature" (60° to 70° F.). The oil is mixed with 1.5 per cent of the drier and subjected to stirring or shaking for 24 hours, the agitation being applied at intervals of an hour. Fused metallic resinates are not soluble in linseed oil at ordinary temperatures, so different treatment is required for them. The oil is heated in an enameled pan together with the finely powdered drier, until the latter is completely in solution, care being taken not to allow the temperature to rise above 390° F. The pan is then removed from the fire and its contents allowed to settle. The quantity of drier used should not exceed 1.5 to 3 per cent. In the case of metallic linoleates (lead linoleate, manganese linoleate and lead-manganese linoleate), the temperature must be raised above 290° F. before they will go into solution. In their case also the addition should not be greater than 3 per cent. Note, after all the tests have settled, the amount of undissolved matter which is left at the bottom, as this is one of the data upon which an idea of the value of the drier must be formed.

B

Solution of Drier in Turpentine or Benzine.—For the preparation of these liquid siccatives 1 to 1.4 parts of the metallic resinate or linoleate are added to the benzine or turpentine and dissolved at a gentle heat, or the drier may first be melted over a fire and added to the solvent while in the liquid state. The proportion of matter which does not go into solution must be carefully noted as a factor in the valuation of the drier. From 5 to 10 per cent of the liquid siccative is now added to the linseed oil, and the mixture shaken well, at intervals during 24 hours.

Samples of all the oils prepared as above should be placed in small clear bottles, which are very narrow inside, so that a thin layer of the oil may be observed. The bottles are allowed to stand for 3 or 4 days in a temperate room, without being touched. When sufficient time has been allowed for thorough settling, the color, transparency, and consistency of the samples are carefully observed, and also the quantity and nature of any precipitate which may have settled out. A note should also be made of the date for future reference. Naturally the drier which has colored the oil least and left it most clean and thin, and which shows the smallest precipitate, is the most suitable for general use. The next important test is that of drying power, and is carried out as follows: A few drops of the sample are placed on a clear, clean glass plate, 4x6 inches, and rubbed evenly over with the fingers. The plate is then placed, clean side up, in a sloping position with the upper edge resting against a wall. In this way any excess of oil is run off and a very thin equal layer is obtained. It is best to start the test early in the morning as it can then be watched throughout the day. It should be remarked that the time from the "tacky" stage to complete dryness is usually very short, so that the observer must be constantly on the watch. If a good drier has been used, the time may be from 4 to 5 hours, and should not be more than 12 or at the very highest 15. The bleaching of the layer should also be noted. Many of the layers, even after they have become as dry as they seem capable of becoming, show a slight stickiness. These tests should be set aside in a dust-free place for about 8 days, and then tested with the finger.