On the Light of Natural Phofphiri, '■ ' t J J • 



cannot be difputed. I have read this (hort treatife with pleafure, from the many excellent 

 and amufing points of knowledge it contains. But on perufing it with a certain degree^ 

 of attention, I cannot avoid making feveral obfervations which the fafts appear to - 

 demand. 



It appears to me that Spallanzani fuppofes himfelfto be the firfl: who obferved that ■ 

 water has the property of abforbing oxygen from the air of the atmofphere. For at the 

 1 14th page of his book, he fays : Trovai pertanto che I'acqua e' un mezzo di decomporrc 

 I'arie, come lo fono il fosforo di Kunckel e i fulfuri alcalini ; ma ella agifce con eftrema Icn- 

 tezza. " I found, however, that water is a medium for decompofing the air in the fame 

 manner as Kunckel's phofphorus, or the alcaline fulphurets ; but it a<fls with extreme 

 flownefs." — But this faft was already known to Scheele (Treatife of Air and Fire), and con- 

 fequently the honour of this difcovery is his right. He was the firft who obferved that, 

 by keeping a bottle of atmofpheric air inverted over water for feveral days, the water 

 gradually rifes ; the volume of air is diminiflied, and azotic gas, or, as it was then called,, 

 phlogiflicated air, remains alone. It is furprifing that Spallanzani fhould not be aware o£ 

 this ; or, if he knew it, that he (hould have omitted mentioning it. 



I have very Important fa£ts to ilate againft his theory of natural phofphori. It Is long 

 fmce I firft obferved that the phofphoric wood not only Ihines under water and under oil, 

 but even in the barometric vacuum ; which obfervations are related in the fecond volume 

 of my theory of heat. If the phofphoric wood require air to enable it to fliine, how can 

 it continue to emit light under oil, where the vital air neither exills nor can have accefs ? 

 I muft likewife remark the difference which Spallanzani has obferved between the urinous 

 phofphorus and that of wood ; namely, that when the former is entirely furrounded by 

 any pure mephitic air, it immediately ceafes to give light ; whereas the other being placed 

 in pure azotic air continues to fliine during fix minutes, and does not entirely lofe its light 

 till half an hour afterwards. 



When Spallanzani introduced phofphoric wood into vital air, or oxygen gas, how did it 

 happen that he omitted to obferve, whether by its fhining in that fluid for a confiderable 

 time, there was no diminution of volume, as he obferved that this diminution took place 

 when the phofphoric flies (lucciole) were placed therein ? 



The luccioloni, or glow-worms, as well as the lucciole, fhine under oil. I have ob- 

 ferved a luminous fly continue to fliine perfectly for a quarter of an hour in the barometric 

 vacuum. 



Spallanzani found that the phofphorus of thefe flies fl>ines much more in oxygen gas 

 than in the air of the atmofphere, and is totally extinguiftied by air not capable of main- 

 taining combuftlon. But how can we explain their ftiining under oil for hours together ?, 

 Thefa£t is certain, becaufe I have repeated the experiment with many variations-; fome- 

 times by putting the phofphoric flies entire beneath the oil, and fometimes the phofphorus . 

 «nly detached from the infcdt, and even cruflied. 



This obfervation muft be well known to you, fince I communicated it laft year to the 

 Royal and Oeconomical Society of Florence, in my Memoir on the Lucciole ; and it will: 

 be equally known to the whole fcientific world, as It will be publiflied in the xjiith volume,- 

 oi the Chemical Annals of the celebrated Bruguatelli. 



T 



^hc 



