which possesses the retention volume of the original corticotrophin. 2. The final product has been characterized and it appears to differ from the original corticotrophin only in possessing a N-terminal glycine residue in place of serine. 3. Preliminary observations that the product has the same corticotrophic activity as the native hormone are quoted. We are grateful to Miss M. B.

A simple apparatus is described for the tensile testing of dilute gelatin gels. Loads are determined from the deflection of a cantilever whilst the specimen is stretched at a constant rate of extension. The extensions can be deduced from the time elapsed. The gels, cast in the form of dumb-bell shaped strips of uniform thickness and matured at constant temperature, are supported by a mercury surface during testing, to minimize deformation caused by the weight of the gel.

Three methods for the determination of the degree of substitution at protein‐amino groups are examined and compared. The procedures are applied to benzenesulphonyl derivatives of gelatin. The formol titration and ninhydrin colorimetric procedures are generally applicable to soluble proteins and their soluble derivatives. The spectrophotometric method is also applicable to these materials when the substituting reagent contains a chromophoric group. In this method the tyrosine content of the protein must be low or not react with the reagent, or the chromophore of the substituent must not absorb light in the tyrosine absorption region. The agreement between the first two procedures is good, and the third method is also in good agreement when the above conditions are met.

The rate of precipitation of Bas04 has been followed conductimetrically. It is shown that the maximum rate of disappearance of ions from solution is dependent on such factors as the total Ba2+ and SO$-ion concentration, the ratio of Bazf to so$ions, and the presence of excess electrolyte. A considerable degree of supersaturation of the soIution with BaZ+ and so$ions appears necessary before reaction and visible precipitation can be detected. For part of the time the reaction appears to be 1st order, and in a certain limited number of cases, it subsequently becomes apparently 3rd order. Measurement of electrical conductance has been used on a number of occasions for the investigation of reaction kinetics, but has rarely been employed in investigating precipitation reactions. Notable exceptions occw in the work of Dutoit,l Harned,2 and Kolthoff.3 pavies and Jones 4 also used this technique to follow the precipitation of AgCl, and observed that the course of the precipitation was influenced by local concentrations of ions at the instant of mixing. It was noted that more nuclei were formed when the local concentration was high, and nuclei of stable size grew more slowly if the ionic ratio was not unity. It was remarked, too, that the kinetics of the spontaneous separation of a substance from its supersaturated solution can be expected to be complex. A private communication by K. E. Howlett indicated that the rate of precipitation of Bas04 was sufficiently slow to be followed by conductimetric methods. Accordingly, in an attempt to elucidate further the processes occurring in such reactions, it was decided to measure the rate of change of conductance with time, of solutions containing Ba2+ and so42ions under conditions in which such factors as ionic strength, ionic ratio, and the concentration of non-reacting molecules could be varied. EXPERIMENTALConductivity measurements were made using a Jones and Josephs type bridge with a Leeds and Northrup valve oscillator as source of current, and telephone with impedance of 530 ohms at 1000 C/S in conjunction with a tuned radio-frequency amplifier as detector. All measurements were carried out at 1000 c/s.The cells were of Pyrex, based on the design of Jones and G. M. Bollinger,s but modified to accommodate a standard B 19 stirrer gland and Pyrex stirrer, the flanges of which were situated centrally above and below the electrodes. The stirrer was generally operated at 150 rev/min except during and, for 20 sec after, mixing the solutions, when the rate was increased to 250-300rev/min. Small changes in this rate did not affect the conductivity or the rate of change of conductivity. The electrodes of the cell used for the more concentrated solutions were platinized, but following the recommendation of Jones and D. M. Bollinger6 bright platinum electrodes were employed for the very dilute solutions. The cells were immersed in a water thermostat at 25" rt: 0*002" C. After each experiment the cells were cleaned first with concentrated H2S04 to remove traces of BaS04, and then with c...

Gelatin has been interacted with benzenesulphonyl chloride and with other sulphonyl chlorides to give sulphonyl‐gelatin derivatives. With dichloro‐s‐triazines, gelatin afforded crosslinked products or monofunctionally substituted soluble products according to the reactivity of the dichloro‐s‐triazine selected and the reaction conditions used; some of the monofunctionally substituted soluble products were reactive towards amines, including gelatin. The properties of the modified gelatins are recorded. Introduction of a sufficient number of hydrophobic groups into gelatin and other soluble proteins conferred diminished solubility in the region of the iso‐ionic point of the derivative, bringing about the separation of a distinct protein‐rich phase (coacervate) from aqueous solution when the pH was adjusted to that region. Some uses of these derivatives are indicated.