>To: S_IZZO@guvax.acc.georgetown.edu
>From: Richard Sullivan <<richsul@roadrunner.com>
>Subject: Re: Van Dyke precip. A Cure
>
>I've noticed this problem as well and there is a good explanation and cure as well.
>
>If you get the precipitate slowly add more tartaric acid until it dissolves. It usually won't take much. Everything will be fine and it will print nicely.
>
>The reason is that ferric ammonium citrate is an ill defined compound. If you look in your Merk Index you will see that it does not have a chemical formula. Every batch may be different. I suspect that the manufacturers are getting *better* at making it.
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>At 01:35 PM 9/7/97 -0400, you wrote:
>> Mac Cosgroves-Davies wrote about getting a white precipitate when
>>mixing a new batch of VanDyke sensitizer.
>> I had a similar problem a few months ago: upon adding the silver
>>nitrate solution to the mixture, it seemed to curddle. I too was
>>using new ferric ammonium citrate. However, mine was from Bostick
>>and Sullivan. I was also using the formula from Keepers of Light.
>> I went ahead and used the sensitizer, shaking it up well each
>>time just before using. I seemed to work all right. (I also let
>>the precipate settle and used the clear liquid on top, and that
>>also seemed to work.)
>> Strangely enough, two days ago I mixed up another batch of VD
>>sensitizer, expecting the same results (same chemicals and formula).
>>This time there was no curddling.
>> I can't explain any of this. My suggestion is to try what you
>>have mixed up. If the results are not satisfactory, try mixing a
>>new batch.
>> Good luck. Suzanne
>>
>>
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