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Tests for Stone

water, atmosphere and stones


The relative enduring qualities of different stones are usually ascertained by noting the weight of water they absorb in a given time. The best stones as a rule absorb the smallest amount of water.

Some stones, however, come from the quarry soaked with water and in that condition are very soft and easily worked. Upon expo sure to the atmosphere they gradually dry out and become very hard and durable. The Bedford limestone of Indiana forms an example of this kind of stone, and the stone in many of the public buildings throughout the United States may be seen in the process of "weath ering", indicated by the mottled appearance of the walls.

To determine the absorptive power, dry a specimen and weigh it carefully, then immerse it in water for 24 hours and weigh again. The increase in weight will be the amount of absorption.

Absorptive Power of Stones Percentage'of Water Absorbed.

Granites 0.06 to 0.15 Sandstones 0.41 " 5.48 Limestones 0.20 " 5.00 Marbles 0.08 " 0.16 Effect of Frost (Brard's Test). To ascertain the effect of frost, small pieces of the stone are immersed in a concentrated boiling solution of sulphate of soda (Glauber's salts), and then hung up for a few days in the air. The salt crystallizes in the pores of the stone,

sometimes forcing off bits from the corners and arrises, and occa sionally detaching larger fragments.

The stone is weighed before and after submitting it to the test. The difference of weight gives the amount detached by disintegra tion. The greater this is, the worse is the quality of the stone.

Effect of the Atmosphere (Acid Test). Soaking a stone for several days in water containing 1 per cent of sulphuric and- hydrocholric acids will afford an idea as to whether it will stand the atmosphere of a large city. If the stone contains any matter likely to be dissolved by the gases of the atmosphere, the water will be more or less cloudy or muddy.

A drop or two of acid on the surface of a stone will create an in tense effervescence if there is a large proportion present of carbon ate of lime or magnesia.