The present work consists of two parts: The first part is a contribution to instrumentation and more particularly the development of a readout system for gas detectors used in small angle X-ray scattering (SAXS) and the second part covers the results of an investigation of interactions between proteins in solution.One aim of the instrumentation part was to investigate the role of fluorescence in gas proportional detector with delay line readout, a phenomenon that leads to events, unrelated to the actual scattering pattern. For this purpose a time stamp (TS-) TDC readout was developed that is able to detect simultaneous events in the detector by using all timing information in the anode and cathode signals (check-sum).It was found that the fluorescence of the gas clearly limits the spatial and time resolution in gas detection. The present observations confirm the influence of argon fluorescence on the point-spread function (PSF) and demonstrate that a rejection mechanism that analyses single events only cannot entirely eliminate these effects. The signal-to-noise ratio can, however, be improved by taking the drift time of the electrons and the check-sum of the signals into account. Drift time measurements are made possible by the unique ability of the TS-TDC to correlate the observation of scattered photons with individual radiation bunches in the storage ring. This feature could also facilitate time-resolved measurements with nanosecond-resolution.In the second part of this thesis gas detectors were used in a contribution to an important topic in biophysics: the study of intermolecular interactions in protein solutions. This was done by measuring the structure factors of protein solutions.According to the DLVO theory the main interactions between spherical particles are the hard-sphere interactions, a short range attraction, due to surface-surface forces, and a long range repulsion caused by the fact that the particles are charged.A computer program was written, which calculates the structure factors from the pair potentials and was shown to reproduce some results in the literature as well as all the main observations in our experiments.Several measurements were made on solutions of the proteins glucose oxidase and lysozyme under various conditions in order to investigate the interactions of these proteins in the presence of co-solutes such as salts, urea, TMAO, glycine or at different protein concentrations. The influence of variables like temperature and pH on the attractive and repulsive interactions and in particular the pair potentials was also studied.The main features of the structure factors observed in the protein concentration series are correctly predicted with the program. The most interesting finding was that salt concentration series of structure factors and the change of the structure factor upon addition of urea and TMAO could be better described if the strength of the attractive potential decreases with increasing salt concentration. Previous work in the literature had relied on a constant attractive potential within a given series of measurements.