The Farmers General held a monopoly of the production, import and sale of tobacco in France, and the taxes they levied on tobacco brought revenues of 30 million livres a year. This revenue began to fall because of a growing black market in tobacco that was smuggled and adulterated, most commonly with ash and water. Lavoisier devised a method of checking whether ash had been mixed in with tobacco: "When a spirit of vitriol, aqua fortis or some other acid solution is poured on ash, there is an immediate very intense effervescent reaction, accompanied by an easily detected noise." Lavoisier also noticed that the addition of a small amount of ash improved the flavour of tobacco.  Of one vendor selling adulterated goods, he wrote "His tobacco enjoys a very good reputation in the province... the very small proportion of ash that is added gives it a particularly pungent flavour that consumers look for. Perhaps the Farm could gain some advantage by adding a bit of this liquid mixture when the tobacco is fabricated." Lavoisier also found that while adding a lot of water to bulk the tobacco up would cause it to ferment and smell bad, the addition of a very small amount improved the product. Thereafter the factories of the Farmers General added, as he recommended, a consistent 6.3% of water by volume to the tobacco they processed. To allow for this addition, the Farmers General delivered to retailers seventeen ounces of tobacco while only charging for sixteen. To ensure that only these authorised amounts were added, and to exclude the black market, Lavoisier saw to it that a watertight system of checks, accounts, supervision and testing made it very difficult for retailers to source contraband tobacco or to improve their profits by bulking it up. He was energetic and rigorous in implementing this, and the systems he introduced were deeply unpopular with the tobacco retailers across the country. This unpopularity was to have consequences for him during the French Revolution.