In this year the first volume of the "West-Country Collections" was issued. Half consisted of Davy's essays "On Heat, Light, and the Combinations of Light", "On Phos-oxygen and its Combinations", and on the "Theory of Respiration". On 22 February 1799 Davy, wrote to Davies Gilbert, "I am now as much convinced of the non-existence of caloric as I am of the existence of light." In another letter to Gilbert, on 10 April, Davy informs him: "I made a discovery yesterday which proves how necessary it is to repeat experiments. The gaseous oxide of azote (the laughing gas) is perfectly respirable when pure. It is never deleterious but when it contains nitrous gas. I have found a mode of making it pure." He said that he breathed sixteen quarts of it for nearly seven minutes, and that it "absolutely intoxicated me."