Re: Dates and names in history

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From: Campos & Davis Photos (photos@campos-davis.co.uk)
Date: 02/14/00-07:14:39 AM Z

This may be a silly question, but if this is a complicated process how
did man find out that dichromate's were sensitive to light? To
produce a dichromate you first have to roast an ore. Does this occur
in nature or is there some natural occurrence which gave someone a
clue about how to produce dichromates? I understand how someone
concluded that ferric processes could be refined, but don't understand
what gave the clue for dichromates.

Campos & Davis Photos
6 Cranbourne Road
London N10 2BT - UK
Tel: + 44 181 883 8638
Fax: +44 208883 8638
email: photos@campos-davis.co.uk
www.campos-davis.co.uk

----- Original Message -----
From: Sil Horwitz <silh@earthlink.net>
To: <alt-photo-process-l@skyway.usask.ca>
Sent: 14 February 2000 06:00
Subject: Re: Dates and names in history

> At 2000/02/14 12:35 AM -0500, Judi wrote:
>
> >On Sun, 13 Feb 2000, Campos & Davis Photos wrote:
> > > Also can someone give me a real definition of what a dichromate
is? I
> > > know how to use them but from what substance do they originate?
> >
> >They're made from chrome.
>
> Come on, Judy, you can do better than that. Sodium dichromate is
made by
> roasting chromium ore with lye (sodium hydroxide). The potassium
dichromate
> can be made the same way, but potassium hydroxide is much more
expensive,
> so the pot dichromate of commerce is usually made by a reaction
between
> potassium chloride and sodium dichromate.
>
>
> Sil Horwitz, FPSA
> Technical Editor, PSA Journal
> teched@psa-photo.org
> silh@earthlink.net
> Visit http://www.psa-photo.org/
> Personal page: http://home.earthlink.net/~silh/
>

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