Vor. 8, No. 10
ELECTRIC METRONOME
2061
molecular weight of diphenyl guanidine being high (21 1.13), large quantities of i t may be used in order t o reduce any possible experimental error. One gram of the base will require 47.3G cc. of 0.1 N acid. Another important advantage of the base is the fact that after its purification by three crystallizations the fine white crystalline substance may be kept in glass-stoppered bottles for years without any alteration. I n our laboratory the purification of the base was performed in 1923, and we are still using i t for our standardization with satisfaction. The purification was carried out according to the method given by Carlton. One hundred gramsof diphenyl guanidine was dissolved in 800 cc. of hot, almost boiling, toluene which was previously dried over calcium chloride and redistilled. The solution was filtered through a hot-water funnel, and the filtrate cooled with vigorous stirring or shaking under running water. The recrystallization was repeated twice more, using approximately 8 cc. of toluene for each gram of the base. The residue of the last crystallization was washed twice on a Biichner funnel with cold toluene, sucked dry, and then dried in an electric oven, first a t 90°C. and finally a t 120" for two hours. The yield is about 80 grams or better. Cold tolueue dissolves the impurities in the base but not the base itself. (I) CARLTON, J. Am. Cham. Sac., 44, 1.169-74 (July, 1922).
ELECTRIC METRONOME I n a n experiment conducted by the laboratory class as a whole i t was necessary t h a t some audible time signal be given regularly so t h a t temperature readings could be taken a t intervals of one minute. By robbing some of the electric impulse which came into the laboratory clock and putting i t into the "line" side of a telegraph relay we were thus able t o operate a local circuit containing a bell and a dry cell so t h a t the desired signal was given. Incidentally, no change in the time of the accustomed "passing" bell was noticed as a result of this tampering. Early Chinese Bronze Distinct from Western Metal. Bronze-making of the early Chinese was entirely distinct from that of the Sumerians who were probably the earliest of the Mediterranean peoples to work in the copper-tin alloy. Analysesof early Chinese bronzes made by William F. Collins, Peiping engineer, and reported to the Institute of Metals. London, lead to this conclusion. The Chinese bronzes contained high percentages of lead, whereas the Snmerian bronze seldom contained more than one per cent of lead. I t is considered by many metallurgists that China developed metal working earlier than, and independently of, western civilization, if bronze casting originated independently. Mr. Collins thinks that it began probably in Kansu. Shensi, or Honan provinces. which are sites of the earliest cultures known in China.-Science Service
