A model is presented for estimating the major element composition of almost any partial melt derived from natural silicate rocks, given that the source composition and physical conditions of melting are known. Another model allows the estimation of water solubility in silicate melts. These models are simple empirical equations based on a database of 1608 experimental results from the literature. The results can be used in the planning of future experimental work or for the interpretation of natural rocks when more accurate methods are not available.