Archived posting to the Leica Users Group, 2000/08/16
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 11:50 AM -0700 8/15/00, Mark Rabiner wrote: >Bill Satterfield wrote: >> >> Tina, the night before I mix anythig, I fill enough graduates with >>water, cover >> them up and leave them in my air conditioned dark room overnight. The >>next day >> the water is a cool 68-70 degrees >> >> Bill( I keep my darkroom cool) Satterfield >><Snip> > >The ruckus I created a week ago somewhere when I insisted "from long >experience" >that liquids in the darkroom will be two degree's cooler than the air. If >my air >thermometer is 71 my trays and even glass bottles of chemicals will pour >out at >69. (degrees) >Turns out though that there are certain basic thermodynamic concepts this goes >up against. >EXCEPT THAT IT IS TRUE. >In every darkroom I've ever worked in and that's a lot!! >First about five people say I'm an amazing idiot. >Then another five or ten (real smart) people say I'm right or close to it! >No metal trays by the way. >I'd attribute it to evaporation and the air thermometer tends to be eye level >while the liquids are kept in the cooler lower levels or on the very cool >cement floor. >Mark's law of thermodynamics: water is cold! >Mark William Rabiner >:) As a liquid evaporates and changes state to a gas it uses energy, in this case heat, from the surroundings to accomplish this. When you dab a highly volatile liquid on your skin, like rubbing alcohol or acetone, the skin will feel cooler almost immediately as the liquid evaporates. Water is not quite as volatile, but the effect that Mark notes is due to the same thing. A container of water, if left open, will be cooler than the surrounding air. Eventually the surrounding air will also cool somewhat. Another factor which affects this is the relative humidity. If the humidity is high, not much evaporation will take place and the cooling is minimal. * Henning J. Wulff /|\ Wulff Photography & Design /###\ mailto:henningw@archiphoto.com |[ ]| http://www.archiphoto.com