Non-Chemical Inquartation Question

[warrendya]

I'm trying my first inquartation just to see how it goes. I melted about 1/2 ounce of silver with approximately 5 grams of a 14k necklace and a watch body I believe to be 10K gold (it tested positive for gold with stannous). I snowflaked the melt in water and added nitric made from sulfuric and sodium nitrate per Steve's recipe, cut 50/50 with distilled water. Immediately upon the addition of nitric the solution became milky white, with no other reaction visible. Upon heating, the white murk coagulated into a white precipitate, leaving a nice blue solution, and the metal pieces began bubbling with small traces of brown gas.

Question 1: if not heated very close to boiling, no reaction is seen with the metal. Is that normal? A few weeks ago I easily dissolved a silver dime in this same batch of nitric at room temperature over a couple of days.

Question 2: what is the white precipitate? it is insoluble in hot or cold nitric acid and hot/cold water. If it was lead nitrate, it should dissolve easily. Lead chloride wouldn't be soluble, but there is no source for chlorine. I verified this by adding some HCL to a sample of the solution and immediately precipitated silver chloride.

Thanks, Dan

 

[lazersteve]

Dan,

I believe the white to be a small amount of silver chloride formed when the nitric and silver reacted. Tap water will do this because of the slight amount of chlorine in it. If it darkens to a purple or gray color when exposed to sunlight it's silver chloride.

The homemade nitric is dilute enough without adding any extra water. The 50/50 recipie is for 70% nitirc acid (to get about 35%).

The delayed reaction may be from too much water in the nitric slowing it down or a silver chloride coating insulating the scrap from the acid (dark shell on the scrap) if enough chlorine was present.

Steve

 

[warrendya]

Good call Steve. I checked the dried filter and the precipitate had indeed turned a very light grey. I put some of the precipitate in a test tube with dilute sulfuric and a nail and lo and behold watched the material turn into metallic silver.

What I don't understand, and the reason I didn't even suspect silver chloride, was that I can't figure out where the chlorine came from. The homemade nitric was made using distilled water, Kragen's battery acid (concentrated through heating & evaporation), and Skylighter/CheapChemicals.com sodium nitrate. I wouldn't have expected any chlorine to be in any of those items.

Good to know for the future, everything's a learning experience. Now I just have to figure a good way to get the gold powder separated from the silver nitrate. They want to stick together when I pour the solution off.

 

[Irons]

commonly contains a small amount of Chloride. Always check it with silver Nitrate solution if Chloride is going to be an issue.

Dissolve a small amount of the suspect Sodium Nitrate and add a couple of drops of Silver Nitrate solution. A white precipitate indicates Chloride present.

Lead contamination will react to form insoluble Lead Sulfate.