"Dumas devised an accurate and excellent method for determining the specific gravities, or densities, of gases which could be used at high temperatures, thus enabling him to experiment upon the vapor densities of iodine, phosphorus, sulphur, mercury, etc. His results, instead of confirming, tended rather to disprove the law of volumes. The trouble lay in the complex nature of the molecules experimented upon, but of course this was unknown to Dumas. He finally declared that even in the case of the simple gases like volumes did not contain equal numbers of chemical atoms. ...The atomic weights determined by him with the greatest care were those of silver, potassium, sodium, lithium, lead, chlorine, bromine, iodine, sulphur, and nitrogen."