472 Transactions. 



These invariably occurred eitlier in marshy places or where there had been 

 extensive accumulation of vegetable matter and a good depth of soil. It 

 is probable that in these localities there is a liberal proportion of those 

 decomposition products which may be included under " humus acids." 

 Low-percentage solutions of acids have many times the conductivity of 

 equivalent solutions of neutral salts or alkalies, and the existence of these 

 in particular localities probably accounts for the comparatively low resist- 

 ances encountered there. 



Further valuable data were obtained from tests of artesian wells about 

 Christchurch. Since these are from 70 ft. to several hundred feet deep, 

 they might be expected to give resistances approaching zero. 



Four wells consisting of 2 in. pipes, 70 ft. to 80 ft. deep, at Addington, 

 gave, on the average, a resistance of 6-2 ohms (A.C. bridge and voltammeter 

 determinations). A 2 in. well, 80 ft. deep, at the city waterworks, Becken- 

 ham, had a resistance of 10 ohms (A.C. bridge). The average of three 

 8 in. wells, 80 ft. deep, at the same place gave resistance of 8 ohms (A.C. 

 bridge). 



Thus these well pipes have resistance of the same order as earth pipes 

 6 ft. deep in the same districts. It would therefore appear that depth and 

 area of pipe in contact affect resistance only to a limited extent. The pure 

 artesian water in the vicinity of the pipe is probably responsible for this 

 eSect. 



A trial was made in sand and shingle ground at Sockburn to ascertain 

 the efiect of treating earth pipes with a higher-conductivity electrolyte — 

 viz., sulphuric acid. Three 1 in. pipes 7 ft. long were placed (well tamped) 

 about 1 to 2| chains apart in much the same class of soil. These were then 

 tested against an independent pipe 1 to \\ chains distant.- These gave 

 individual resistances as follows (A.C. bridge test) : The earth-resistance 

 of the first pipe, on treatment with 5-per-cent. sulphuric acid, fell from 

 460 to 170 ohms — -i.e., by 63 per cent. ; that of the second, on treatment 

 with 15-per-cent. sulphuric acid, fell from 910 to 350 ohms — i.e., by 61-5 

 per cent. ; that of the third, on treatment with cold concentrated sodium 

 chloride, fell from 360 to 170 ohms — i.e., by 52-8 per cent. 



The higher-conductivity solution gives a bigger reduction of the initial 

 resistance, but soil, though mechanically uniform, is apparently so variable 

 chemically that a great many tests would be necessary to give a definite 

 result. The degree of penetration into the surrounding soil and the 

 composition of the soil are both very uncertain. There was, of course, 

 considerable action of the acid on the pipe, and there is no suggestion 

 whatever to use such a method commercially. 



It has been previously stated that the resistance lies almost wholly 

 within a radius of a few feet of the pipe. This is shown clearly in diagrams 

 Nos. 3 and 3a of the resistances obtained in different localities between 

 pipes at varying distances apart. The effect of saturating the ground round 

 these pipes with an electrolyte (a strong solution of sodium chloride) is also 

 shown by these curves. The Wellington pipes were 3 in. pipes, 6 ft. long, 

 and were placed in reclaimed ground with a good admixture of surface 

 soil. The Addington pipes 'were 1 in. in diameter and 10 ft. deep, driven 

 in peaty to sandy soil. The pipes at Bealey Corner were l^in. and l|in, 

 pipes, 6 ft. deep. At Sockburn 1 in. pipes were placed in shingle and sand 

 over 7 ft. deep. The pipes from which curve 3a was obtained were placed 

 in line in the same class of soil. The pipes were all salted with 4 gallons 

 ■ of cold concentrated brine poured into each. When salting, the most dis- 



