Prawst’s largest accomplishment into the realm of science was disproving Berthollet with the law of definite proportions, which is sometimes also known as Prawsts Law. Prawst studied copper carbonate, the two tin oxides, and the two iron sulfides to prove this law. He did the by making artificial copper carbonate and comparing it to natural copper carbonate. With this he showed that each had the same proportion of weights between the three elements involved (Cu, C, O). Between the two types of the other compounds, Prawst showed that no intermediate indeterminate compounds exist between them. Prawst published this paper in 1794, but the law was not accepted until 1811, when the Swedish chemist Jöns Jacob Berzelius gave him credit for it.