Dec,, I92I.] CURRENT TOPICS. 84I

Corrosion of Metals in Alkaline Soi ls .BW. NELSON SMITH and J. W. SHIPLEY presented at the tenth general meeting of the Engineering Institute of Canada, Saskatoon, August i i , I92I , a paper giving an account of extended experiments on the corrosion of metal conduits by soil solutions. The paper appears in full in a recent issue of the Engineering Institute's Journal. The con- clusions are :

t. The corrosion of cast iron by the salt solutions found in natural soil is readily accomplished under natural conditions without access of stray current. The corrosion is of the so-called.graphitic pitting type by which is meant the commonly observed condition of the material remaining in place, which is invariably of a soft spongy texture with part of the iron dissolved out, the remainder re- sembling graphite in consistency.

2. Magnesium salts are the most corrosive of the soil salts, and magnesium sulphate, which was found wherever a cast iron pipe had been destroyed, is apparently the most effective of the salts ex- perimented with.

3. Local action induced by naturally occurring concentration cells may easily be a factor in tile pitting of cast iron exposed to salts of varying concentration.

4. Slight pitting corrosion was found in pieces of cast iron ex- posed to the action of small samples of wet soil and intermittently heated, even in the short period of forty days, and with only a limited supply of water as compared with conditions in natural ground, no impre~,:sed e.m.f, being present. It . L.

On the Velocity of Sound in Gases at High Temperature and the Ratio of Specific Heats. H. B. DixoN, COLIN CAMPBELL and A. PARKER. (Proc. Royal Soc., A 7o2. ) - -The time required for a sound wave to traverse }he gas contained in a tube of known length was measured by a pendulum chronograph. The material of the tube was selected so as to avoid chemical action between the contained gas and the tube. For air and carbon dioxide it was desirable to have a tube of fused silica. This was difficult to get since the length was to be I4 meters. The Thermal Syndicate of Newcastle-on-Tyne ac- complished the task, and though the first two long tubes coiled into spirals broke in transit and the third broke upon heating the fourth proved satisfactory.

The velocity of nitrogen was measured up to ~ooo ° C. for which temperature the value of 696.8 m. per sec. is given. At o ° C. it is 334.4. The velocity in air was determined up to 7oo ° C., while 6oo ° is the limit for carbon dioxide and methane. From the velocities in the tube the velocities in free air are calculated. The data for specific heats at constant pressure and at constant volume are also tabulated. The ratio of the former to the latter in the case of nitrogen sinks from z.4o8 at o ° C. to 1.374 at ~ooo ° C. G . F . S .

VOl_ 192, No. II52-~0