PROFESSOR 0. MASSON ON IONIC VELOCITIES. 
343 
made with other chlorides and Avith other copper salts, this value for p' can not be 
far wrong. 
Expenmental DetaUs. 
The fblloAAnng facts, in addition to those already stated, may be recorded concerning 
the series of experiments, the results of which are tabulated in this papei-. 
Gelatine. —The small conductivity of this has been already referred to. As 
additional evidence that its impurities are unimportant, it may be mentioned that 
practically no difference is observed in the value of ujv got for the same concentration 
of the same salt, Avhether the jelly contain, as usual, 12 per cent, of gelatine or only 
half that amount. 
Salts .—-The salts used Avere all re-crystallized, and Avere Avhat is generally called 
pure ; but no very special purification Avas attempted, as the present object Avas rather 
to test the method in a preliminary maimer than to get the most accurate quantitatiAm. 
results attainable. 
Jellies.—These Avere made as folio aa's. The required quantity of the salt Avas 
Aveighed into a beaker, dissohmd in Avater, and Avashed into a stoppered 50 cub. centim. 
flask containing 6 grammes of gelatine in small pieces. The flask Avas AAmrmed till 
the gelatine had dissolved, Avater AAms added to the mark, and the contents mixed and 
cooled. The exact volume AAms then made up Avith Avater and, after re-warming and 
thoroughly mixing, the jelly AAms ready for use. It Avas always made fresh for each 
experiment. For the experiments Avith lithium chloride, which is very deliquescent, 
the calculated quantity of carbonate Avas dissolved, Avith all precautions, in slight 
excess of hydrochloric acid, and the chloride AAms obtained neutral in reaction by 
evaporation and drying at about 150 ° C. The jellies Avere all clear Avhen solid and 
Avere transparent in the tube ; except the tAvice-normal lithium sulphate one, Avhich 
Avas, in bulk, Amry slightly opalescent. The melting-points Avere by no means all the 
same, but all Avere completely solid at the temperature employed. 
Temjyerature of the Bath. —This Avas in all cases very close to 18 ° C., the average 
in each experiment lying beloAA^ rather than aboAm that point. The extreme variation 
during any experiment did not exceed ' 5 ° on either side of 18 °, and was generally less. 
Cell-solutions. —These AA^ere ahvays of normal strength, i.e., the anode cell contained 
CuSOi gramme per litre, and the cathode cell contained K2Cr04 + KoCiqO? 
gramme per litre. Each cell contained 100 cub. centims. 
The Tube. —This AAms the same in all the experiments tabulated. Its ends Avere 
ground smooth, and its bore uniform. Its length Avas 15 centims. and its area of 
cross-section (A), Avhich Avas determined carefully by the Aveight of its mercury 
contents, Avas ‘0378 sq. centim, It was divided into half centims. on both sides to 
avoid parallax, and the scale diAusions were picked out Avith red. They Avere easily 
seen througli the AAmter against the Avhite porcelain bottom of the bath. It was quite 
possible to divide by eye to less than half a millim. ; but only the readings made 
