High-pressure physics, the study of the effect on matter of extraordinary pressure and techniques required to achieve and measure such pressure. The development of high-pressure physics affords a striking example of how science, by continually building on its achievements of the past, progress at continually accelerating rate. The beginning of high-pressure physics as subject of serious scientific endeavor go back nearly two hundred years to experiments by Jon Canton (1718- -1772) published by the royal society of London in which he established that water is measurably compressible, not incompressible as had been supposed. The next important experiments were not made for nearly fifty years. After this the rate of the progress gradually picked up, and by the end of the nineteenth century there where important center of activities in England, France and Germany. Early the twentieth century important activities spread to the United States, and now are being conducted in many laboratories in both academic and industrial all over the world, under an increasingly wide range of pressure and with increasingly important results. We should bear in minds that pressure is defined as force per unit area, and is not the same as force itself. A very high pressure maybe produced by a relatively small force if it is applied in a very small surface area.
Problem of Techniques. There are many difficulties in high-pressure experimenting, and the initial slowness of progress was in large part due to the slowness with which the problems of techniques were solved. There are at least three types of this problems: the problem of preventing leakage of the liquid in which pressure is generated and by which it is transmitted; the problem of preventing the vessel containing the pressure from bursting under the action of pressure; and the problem of accurately measuring the pressure and its various effects. These problems have by now been solved to a large extent, and even on those case where present solutions are inadequate, the principles are understood on winch a more precise solution depends.
Effect of High-pressure. Extensive investigation of the effect of pressure on various physical properties of matter have been made by a writer in the years 1908 – 1956. In the range up to 30,000 atmosphere it was posible to study nearly all the physical properties of many substances in the general classification of room temperature. In the range of 30,000 up to 100,000 atmosphere and sometimes beyond, the measurements were more limited in scope, but it was possible to study the effect of pressure on the volume, electrical resistance, and phase changes of nearly all the elements and many other substances, all temperature within a few hundred degrees of room temperature. Most of the phase changes induce by pressure are reversible, so that when pressure is released, the material reverts to its original condition. There are however , a few instance of irreversible changes produce by pressure. One example is a phosphorus, which maybe permanently altered by pressure a few tens of thousands of atmosphere, becoming black and conductor of electricity, with a density 50% greater than its original yellow form.