Is it zinc or aluminium?

Other than melting temperature, is there a quick/simple way to distinguish between zinc and aluminium?

If I throw a bit of gray metal into the melt pot and it is zinc when I was expecting that is was aluminium, the resulting casting will be spoiled.

What do others use to keep these metals separate? The alchemists must have had some simple method of testing their bits of metal.

Paul

Paul,

Weigh it; then check the volume, and calculate the Density.

... Remember Archimedes ?

Table of densities here [and many other places]

MichaelG.

and aluminium reacts with caustic soda.

Also try making a battery with a bit of copper, mystery metal and acid. You could calculate resulting voltage but comparison with known sample would be easier.

Aluminium should not react with vinegar at room temperature. Zinc will react slowly giving of bubbles of hydrogen.

Aluminium and zinc will react with strong (15%) caustic soda solution evolving hydrogen at room temperature magnesium will not.

Clean zinc and magnesium both react rapidly with copper sulphate depositing copper on the surface of the metal but aluminium does not.

If you heat zinc strongly with a blowtorch it will vapourise and oxidise emiting a white smoke. Aluminium does not do this. Magnesium will burn with a bright white flame if heated strongly and give of white smoke.

Mike

Bazyle.

can you still get caustic soda ? I thought that had been banned years ago. But was a great week killer.

Dave.

Oops. Weed killer sorry. Predicted text.

Dave.

Yes caustic soda is easy to get. You're thinking of sodium chlorate which, as well as being a weedkiller can be used in various recipes to make bombs.

Russell.

Sodium Chlorate was banned by the dicks in Brussels years ago as a fire hazard and yes it was a good weed killer and also an ingredient in the making of gunpowder/black powder [ as a replacement for sodium/potassium nitrate] so as the Americans say 'go figure'

Tony

Sodium Chlorate available in liquid form over here. Crystals only sold in tins from under the counter now, along with Carbon Tetrachloride. (Old stock guvn'r.)

Potassium nitrate was certainly available ten years ago and may still be, albeit in small quantities. It's an essential ingredient for curing ham and bacon.

Aluminium, Zinc, and Copper will all react with Caustic Soda.

Mercury will react with Aluminium, to produce "whiskers" but you are not likely to be able to get hold (no pun!) of any, because it can be quite dangerous to health (especially Kidneys).

Aluminium swarf will burn, (so will Magnesium - BIG time) BE VERY CAREFUL, where, when and how and how much, you test.

I would not expect Zinc or Copper swarf to burn.

The melting points, may give a clue as to Ali or Zinc, but the purity will cause variations in the actual value.

Howard

Hi there, all,

You can determine the specific gravity of an object using just a rigid rod, three bits of string, a counter-weight, a measuring tape and a bucket of water.

Suspend the rod by roughly the centre using one piece of string, hang the counter-weight on one end and the object from close to the other end using the other two pieces of string. Arrange the object, counter-weight and 'centre' suspension positions until the system is in balance. Measure the two spacings between the suspensions of the object, the counter-weight and the main suspension point.

Then lower the system so that the object is freely immersed in the bucket of water and not trapping any air bubbles - adjust one but not both suspensions to restore balance. (It's best if you only move the object, you'll have to move it further from the main suspension - leave the counter-weight position unchanged wrt the main suspension.)  Measure and note the new inter-suspension distances. The object will have 'lost' the weight of its volume of water.

By a bit of algebra, the specific gravity of the object can be calculated (I'd describe the details of the calculation here but it's a bit too close to bed-time!).

Look up the specific gravity in the reference books or on the Internet to get a pretty reliable clue as to the metal's identity.

This method may sound a bit Heath-Robinson but it's certainly capable of distinguishing between aluminium (alloy) and zinc or die-casting metal.

Best regards,

Swarf, Mostly!

Edited By Swarf, Mostly! on 09/11/2013 22:51:26

Edited By Swarf, Mostly! on 09/11/2013 22:52:40

Caustic soda will not react with copper.

Mike

When I was involved with die-cast parts years ago, in both aluminum and zinc we just used to pick them up to find out which was which. Zinc is pretty heavy compared to aluminum. Close to steel actually.

.

Quite so ... as per my first reply.

I presume that others are just fond of their Chemistry sets.

MichaelG.

... er .... yeah ..... sans the weighing, checking the volume and calculating the density I guess it is.

(Sorry, Michael - couldn't resist).

.

Yes ... exactly

Your experience allowed you to estimate the density; thus skipping those formal steps.

That's a reasonably safe thing to do ... because the difference in these densities is roughly 3:1

Paul was obviously unaware of this, so I was trying to help him understand the principle.

... finding the shortcuts comes later.

MichaelG.

How about soft solder? If its sheet then zinc will 'tin' fairly easily but ali will not. Not so convenient on lumps which I guess was the OPs situation.

SteveW