Monday, 18 August 2014

Sheep of the month - August 2014

Awassi sheep grazing on stubble. Image: Ferrell Jenkins

Breed notes
Awassi sheep are hardy, with a red head and legs, convex face and drooping ears. They are a fat-tailed sheep breed, having the characteristically heavy tail and hindquarters with fat storage deposits. Males are horned and females mostly polled. Awassi fleeces are double-coated with plenty of kemps, in a range of colours from white to brown. Ewes produce relatively large quantities of milk compared to other breeds. Awassi are the most numerous and widespread sheep breed in the Middle East.

Isotope notes
The image shows livestock grazing on the remains of a crop after the grain has been harvested. This manures the field as well as providing late summer/early autumn nutrition for the grazers. This practice will be isotopically visible only if the harvested crops are isotopically distinct from the plants the animals normally eat. Potential examples include: peas or beans in areas with little clover in the pasture (as legumes and non-legumes are isotopically distinct); C4 crops such as maize, millet, sorghum or sugarcane in predominantly C3 plant areas; or if the field crop has been heavily manured. 

Monday, 4 August 2014

What happens to wool samples in the lab? Part 3

After washing and grinding, the sample needs to be got ready for the analysis itself. When being loaded into the mass spectrometer, the powder is contained in capsules made of pressed metal foil:
Unbelievably tiny capsules
These are both 3.5 mm across by 5 mm high. The one on the left is made of tin (for carbon and nitrogen isotope value analysis) and the one on the right is made of silver (for hydrogen and oxygen isotope value analysis). As you can imagine, loading sub-microgram amounts of highly static hair powder into these is a recipe for madness... especially if you've got to do scores of them in triplicate....

Microbalance plus tools
We weigh exactly how much sample is in each capsule. We do this on a very sensitive balance. The object to be weighed is placed on the small round platform you can see inside the perspex cylinder. This is then closed so that no air movements can disturb the weight. I am loading pinches of hair powder with the very fine tweezers you can see. I clean these between each sample using methanol, which is in the orange-labelled squeezy bottle.

Lab book with weights and trays with samples
Storage tray close-up
Once we've got the right amount of powder in the capsule, we fold it tightly to stop it falling out again. Then we put the folded capsule in a storage tray. These have 96 little wells, so one sample goes into each. The weight of the sample in each well is recorded. We can then take (or send) the samples to the lab where the actual analysis will be done.

Next: running the analysis. This next post will have to wait for a bit, as I won't be doing this for a few months...

What happens to wool samples in the lab? Part 2

Once the samples have been washed, they are dried and ground. Grinding hair samples is tricky, as they're very elastic. To do this, we use a machine called a ball mill.
Loading wool into a ball mill cartridge
The wool fibres, which are 5-20cm long in the fleece, are cut into ~1cm lengths. Then they are loaded into the steel cartridge with a grinding ball. The machine shakes the cartridge so that the ball crushes the other contents. Note that I'm handing the samples with tweezers: this is partly to make sure they're kept as clean as possible, but mostly because the fibres are very static and stick to my gloves...

Milled wool 
And here's the result after a minute or so: wool powder. Like the whole fibres, this is usually static as anything, so it needs really careful handling to stop it jumping about!

Next: weighing into unbelievably tiny capsules in Part 3.