To Test the Purity of Turpentine.
—It is of considerable importance that turpentine used for painting should be quite pure. To test the purity in a practical way pour a few drops on a sheet of white writing paper; if it is pure the mark will evaporate in a few minutes, leaving the paper quite clean. If, however, paraffin oil has been added to the turpentine it will leave a greasy mark on the paper, which will not disappear for several hours or even days. Turpentine is sometimes adulterated with benzine. The test above will not detect this, as the benzine will not leave a greasy mark. The evaporation, however, will be more rapid than when the turpentine is pure. When turpentine is very old, it becomes “gummy” or thick, and is unsuitable for mixing with paint. This condition is indicated by a greasy mark left on writing paper when a few drops are poured upon it.
Another very simple test for the purity of turpentine is to place a sample in a small white bottle and shake vigorously, carefully observing the time that it takes the bubbles that arise from the agitation to disappear. If the turpentine is adulterated with paraffin oil the bubbles will hold longer than when it is pure. The best plan is to have a bottle containing pure turpentine and another containing the suspected sample, and to shake up both together, comparing the rapidity with which the bubbles disappear.
Paraffin oil is also sometimes detected by smell: pour a couple of drops on the palm of the hand, rub the two hands briskly together, when the characteristic smell of paraffin will be easily detected if any considerable amount be present. Turpentine is sometimes adulterated with rosin spirit, and this can only be detected by means of analysis.