The inventor of Mayer's reagent and one of the founders of thermodynamics, Julius von Mayer was the first to enunciate what phrase, known as the first law of thermodynamics?
Mayer's reagent Mayer's reagent is an alkaloidal precipitating reagent used for the detection of alkaloids in natural products. Mayer’s reagent is freshly prepared by dissolving a mixture of mercuric chloride (1.36 g) and of potassium iodide (5.00 g) in water (100.0 ml). Most alkaloids are precipitated from neutral or slightly acidic solution by Mayer’s reagent (potassiomercuric iodide solution) to give a cream coloured precipitate. This test was invented by the German Chemist, Julius Robert Von Mayer (1814–1878).
Émilie du Châtelet Gabrielle Émilie Le Tonnelier de Breteuil, Marquise Du Châtelet (] ; 17 December 1706  – 10 September 1749) was a French natural philosopher, mathematician, physicist, and author during the early 1730s until her untimely death due to childbirth in 1749. Her most recognized achievement is her translation of and commentary on Isaac Newton's book "Principia" containing basic laws of physics. The translation, published posthumously in 1759, is still considered the standard French translation today. Her commentary includes a profound contribution to Newtonian mechanics—the postulate of an additional conservation law for total energy, of which kinetic energy of motion is one element.