6 Samples 10–18 were prepared in our laboratory using a revised version of the precipitation method established by the ISF Institute in Germany.6 7 Th is method obtains a precipitate through the addition of BaCl2.2H2O; the resulting precipitate can be washed and stored easily. 8 Th e samples were subsequently shipped to ISF for analysis by accelerator mass spectrometry (AMS). 9 All tubing used was stainless steel, and although two samples were at risk of CFC contamination as a result of brief contact with plastic, variation among samples was negligible.
Methodology — Grammar and Writing Skills 47 2.2.1 Passives and tense pairs When a sentence changes from active to passive, it looks like this:
Th e dog bit the policeman. active
Th e policeman was bitten by the dog. passive But in formal academic writing, when you report what you did, you don't write 'by us' or 'by me' when changing the sentence from active to passive. You simply leave the agent out, creating an agentless passive:
We/I collected the samples. active
Th e samples were collected. passive Before you begin to write the description of what you did and used, you need to check with the Guide for Authors in your target journal (if you are writing a doctoral thesis in an English-speaking country, check with your supervisor) to fi nd out whether this part of the paper or thesis should be written in the passive or in the active. You can use the active (we collected) if you worked as part of a research team. Using the active is not usually appropriate when you write your PhD thesis because you worked alone, and research is not normally written up in the fi rst person singular (I collected). In most cases, you will fi nd that in papers and theses, the procedure you used in your research is described in the passive, either in the Present Simple passive (is collected) or in the Past Simple passive (was collected). To make that choice, it is useful to explore the advantages and disadvantages of each. Th ere are two common errors in the way passives are used in this section. First, look at these two sentences: (a) A fl exible section is inserted in the pipe. Present Simple passive (b) A fl exible section was inserted in the pipe. Past Simple passive When you write about what you did and what you used, you need to be able to distinguish between standard procedures, i.e. what is normally done or how a piece of equipment is normally constructed, and what you did yourself. In the examples above, (a) uses the Present Simple tense to describe what is normally done or to describe a standard piece of equipment used in the research and (b) uses the Past Simple tense to describe what you did yourself. It is conventional in this section to use the passive for