The free‐radical polymerization of phenylacetylene initiated by azobisisobutyronitrile at 50°C was studied in bulk and in the presence of benzene and toluene. The polymerization rate is approximately first‐order with respect to the initiator concentration. The number‐average molecular weight of the polymer is independent of the initiator concentration in bulk and is approximately proportional to the monomer concentration in the presence of the two diluents, but independent of their nature. The data are consistent with a mechanism based on first‐order decay of active to inactive radicals. This step appears to exert the major control over kinetic and molecular chain lengths. Chain transfer to the monomer is concluded to be absent or to make only a small contribution to molecular termination.

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The basic concepts of optical absorbance and transmission are readily demonstrated by the student in a series of colorimetric titrations carried out in a titration cell installed in a rapid scanning spectrocolorimeter. The student observes color changes in the titration cell and relates them to the spectral transmission curve of the solution, which he sees simultaneously on an oscilloscope. The process of formation of new species at each stage of the titration can be followed. The student can also readily demonstrate isosbestic points. A further method is presented for determination of the endpoint of a titration by simultaneously comparing the absorbance of the liquid at any two wavelengths in the visible region.

Minor decreases in the vapor pressure of water in solution were accurately determined using a newly established method. The decreases were found to be linear with solute concentration in the range 0.02–0.1 molal. A slope for the decrease of vapor pressure for one molal solutions based on single particles was calculated and compared with the slope generally expected according to Raoult's law. The differences were found to be proportional to the charge and radius of the solute particles. An experimental rule was formulated. It provides a good fit for electrolytes, nonelectrolytes, and polyelectrolytes. The results are interpreted according to a standard state, P°i, for the vapor pressure of each solution at 10−3 molal. It is assumed that the solution obeys Raoult's law in the range 10−3−10−1 molal, substituting P°i for the vapor pressure of water. P°i is smaller than P° by about 0.2% for electrolyte and 1.5% for polyelectrolyte solutions.

A recently developed empirical method for the determination of solute parameters by solvent vapor pressure measurements is further explained and demonstrated. The results of our laboratory and those of two other laboratories have shown that the osmotic coefficient of water is practically constant over the range 0.02–0.1m. This is consistent with the above-mentioned method. Examples are given for solutions of simple electrolytes, polyelectrolytes, and complex ions.