Experience with the usual types of glass pyknometers long ago convinced the writer that these instruments as ordinarily used are subject to considerable errors and may be quite unreliable when dealing with small quantities of material, It is true there are forms intended to be used in conjunction with a very precisely regulated water-bath which are capable of giving results of high accuracy, but this method of determination at constant temperature involves too much time and trouble for routine mineralogical work. But no matter what the design of glass pyknometers, and their variety is legion, in actual practice they suffer in common from tile defects of the material of which they are constructed.

The heavy-solution method is inconvenient ; it cannot be used for the heavier materials and there is often danger of contaminating the material which may be intended for analysis.