The object of the work described is to determine whether, in any nickel compound, the paramagnetism of the nickel is approximately neutralised by the diamagnetism of the molecule, so that it might be possible to change the sign of the susceptibility by temperature change alone. A method for measuring small susceptibilities has been developed which, in comparison with current methods, uses simpler apparatus, and simplifies the taking of observations, without prejudice to accuracy or sensitivity. The susceptibilities of a number of nickel compounds have been investigated. It is found that the susceptibility is profoundly affected by the nature of the chemical valence link. In polar compounds the nickel retains a practically constant paramagnetism which is considerably larger than the underlying diamagnetism, and it is hence concluded that such compounds are unsuitable for investigations of change of sign of susceptibility by change of temperature alone. It is suggested that the investigation might be carried out on certain nickel dioxime compounds. The results indicate an abnormality in the structure of nickel cyanide.